The older non-learning Producer 8 (model number URC-8090) doesn't fetch that much on ebay, so that's the best place to start, sometimes you can even find people selling broken ones, which would suit you perfectly.

On the other hand, it probably wouldn't be that hard to build one from scratch. You can get the schematics etc on the FCC web site (grantee code: DI2, equipment code: 9800)

Rob