You can find it at www.emu.com
They should list it under products. If it is not there, it may be in a historical archive that they have on the site of their older products. Sorry, but I can't remember exactly how to get there other than through the main page.
The E-64 is based on E-mu's E-IV samplers. Most options, I believe, are available for it except it cannot be turned into an Ultra model and it uses older 30-pin SIMMs instead of the 72-pin SIMMs. All of these are getting harder to find nowadays but there are a few places that you can still get it from. I don't know if the ROM boards (E-Synth, etc) are available for it either. Also, the new R-FX chip will not be available for it.
Unless you're getting it for a steal, it may be more worth it to go for an E-5000 Ultra or a E6400 Ultra. With it being used and older E-mu techology, I wouldn't pay more than $900 US myself. If it came more stock, this number would come down but, with the 1 GB HD and Digital I/O option it brings the price up slightly. It is quite a capable sampler but the newer ones are speedier (because of the Ultra processor) and can be upgraded more. Personally, I'd like the upgradability of the newer samplers.