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via
these auctionsSSM2044 Resonant Lowpass filter chips
SSM2056 Voltage controlled envelope chips
SSM2045 Voltage controlled filter & VCA "Voicing System" chips
You'll also find an Electronics learning toolkit in the listings.

Regarding the SSM chips: "These were pulled from a Korg Polysix that had the main board destroyed by leaking memory backup battery... These are used in some Emu and other Korg vintage synths. Also, these are useable in many modern DIY projects that you can buy kits to built up. The choice is yours... Date stamped 8238" See
Synthesis Technology's chip page for a list of chips used by various synths.
Update via Qwave in the comments: "There is no Waldorf synth with these chips." This is correct, some used CEM chips for the filter. You can see a list
here. Waldorf removed from the description above.