via
weisma where you'll also find a 2600 and 1611 sequencer.
"In the 1960s I was one of the
pioneers of contemporary electronic music in the Netherlands. In the 1970’s, when the portable ARP 2600 synthesizer was created by ARP Instruments, Inc., I decided to start my private electronic music studio “Five Roses”, using the ARP 2600 for studio compositions as well as live electro-acoustic performances. At a later stage, when the modular ARP 2500 synthesizer was introduced, I expanded the capabilities my studio step by step.
The ARP synthesizers have been the center of my work for many years, but as electronic music became mainstream, my focus shifted to acoustic contemporary music. It is therefore that I have decided to put up my now classical ARP 2500 and 2600 synthesizers for sale for the collector, or for the musician that wishes to explore the unique sound of these landmark analog synthesizers."
Details on the 2500:
1974 2515 Studio Cabinet with 15 module positions
SN 74-005
Modules:
"1002 Power Supply
SN 1974/30262
Power supply included with the cabinet.
1004T Voltage Controlled Oscillator
SN 1976/50246
Single precision voltage controlled oscillator offering five simultaneous waveform outputs: sine, triangle, square, sawtooth, and pulse. Provides frequency modulation, pulse width modulation and built-in waveform mixer. Also provides inverted waveform outputs.
1005 Modamp
SN 1976/40551
A complex function module containing a precision balanced modulator, a voltage controlled amplifier, and switching circuitry.
1006 Filtamp
SN 1977/30231
A combination of a voltage controlled low pass filter, a voltage controlled amplifier, and a mixer.
1016 Dual Noise / Random Voltage Generator
SN 1976/40480
Contains two independent noise sources and filters to derive pink noise and continuous slow random voltages. Slightly weak signals from both noise generators. Very weak signal from slow random noise generator A.
1023 Dual Voltage Controlled Oscillator
SN 1977/40266 Two precision voltage controlled oscillators offering five simultaneous waveform outputs: sine, triangle, square, sawtooth, and pulse. Provides frequency modulation, pulse width modulation, and built-in waveform mixer.
No signal from left oscillator.
1027 Ten Position Sequencer
1974/30250
Flexible sequential voltage generator. Capable of creating complex switching patterns with 30 preset voltages.
1033 Dual Delayed Exponential Envelope Generator
SN 1977/50122
A flexible envelope generator that includes a variable trigger delay.
1036 Dual Sample & Hold / Random Voltage Generator
SN 1977/50232 Contains two low-drift sample and hold circuits, two noise sources, and two voltage controlled pulse generators.
1045 Voltage Controlled Voice
SN 1974/30247
Combination of two Envelope Generators / Voltage Controlled Oscillator / Voltage Controller Filter / Voltage Controlled Amplifier. Used as preset voice.
1047 Multimode Filter / Resonator
SN 1974/30258
Combination high-pass, low-pass, band-pass and band-reject filter. Ultra-high Q. Voltage controlled center frequency and resonance.
1050 Mix/Sequencer
SN 1974/30053
A combination of a sequencer, mixer, and analog gate. Serves dozens of functions as a utility mixer, sequencer and preset function selector. This module is linked to the1027 sequencer module.
See
Donald Tillman’s page of resources and articles on ARP Synthesizers and
Guitar Fool’s ARP 2500 Synthesizer Pages for more information, including manuals and schematics."
All modules are working and sounding fantastic. The filters are especially lush, definitely nothing else sounds like a 2500 and the unique matrix switch system is ripe territory for happy/accidental patching discoveries. 
via weisma where you'll also find a 2600 and 1611 sequencer. 
The ARP synthesizers have been the center of my work for many years, but as electronic music became mainstream, my focus shifted to acoustic contemporary music. It is therefore that I have decided to put up my now classical ARP 2500 and 2600 synthesizers for sale for the collector, or for the musician that wishes to explore the unique sound of these landmark analog synthesizers." 
via this auction
It includes the following modules-
Internally- According to Phil's description when he sold it, the power supply had been upgraded about 2 years prior to my friend buying it to a 1.5 Amp, low noise high performance unit. The separate 12v lamp power supply had also been rebuilt around that time.
This one spotted and sent in via Jimmersound.
via this auction
"super-rare ARP 2500 from the personal collection of Phil Cirocco of CMS / Discrete Synthesizers. It features a rare, vintage ARP 2002 cabinet, a 3000 series four voice keyboard and a full compliment of 1000 series modules. This is a once in a lifetime opportunity to own a fully functional, killer sounding synthesizer, as well as a rare piece of electronic music history. The 2002 cabinet is in good condition. It is all original and has not been restored. It was made in 1970. It is a very early and rare version featuring 10 patching tracks on the top section instead of the 20 that later versions use. The top section of a 2500 is only used for CV, gate and trigger etc. so 10 tracks is usually adequate for most situations. It has 20 tracks on the bottom as all 2500s do. Also, this early unit is more compact and uses its space more efficiently than later versions. (Many people complain about the large amount of real estate that later version 2500 cabinets use up.) The power supply was upgraded here at CMS about 2 years ago to a 1.5 Amp, low noise high performance unit. The separate 12v lamp power supply was also recently rebuilt. The Keyboard is a standard ARP 2500 4 voice split keyboard. The rubber mounts of the key contact PCB have been replaced. The key contacts have been cleaned. The rubber pads of the keyboard are intact. The keyboard is fully functional. The keys are in very good condition. The hardwood keyboard cabinet is in very good condition. There is a very small ding on the left keyboard control panel. It includes the keyboard connection cables as well as the AC cable. The 1000 series modules are fully functional and have been meticulously maintained here at CMS for the past decade. The module compliment includes the legendary ARP 1047 Multimode Filter and the ARP 1027 sequencer. The 1004T VCO and the 1036 Dual Sample Hold were originally owned by the ARP factory as production samples. The dual VCO is a super-rare prototype developed at ARP by Roger Powell and Clark Ferguson.
1004T VCO
