It appears that there are currently a few synth chips available on eBay, lots of 10 programmable sound generator Yamaha AY-3-8910 chips! for mere $12 US. More info available on this dedicated site as well as the datasheets. Also found are a few SN76477Ns, one of them still in the original Archer package for only $6.95 so snag it now, sn76477N.