Recommendation for a USB digital simulator
The product you're looking for is a digital pattern generator. While this one is overkill for your specification, it's the one that I'm most familiar with. It'll probably set you back about $12-20k for a full setup. 

Basically their setup is a FPGA hooked up to a bunch of RAM driving 16 logic outputs. It's really fancy because you can set the frequency and output voltage of the module. Cheaper, slower, and less-flexible modules should be available from someone else.