I really can't see the purpose of the "backyard gardener" requesting germplasm from the USDA/GRIN. I have fairly easy access to probably a thousand different kinds of extremely tasty tomatoes from all over the world in catalogs or trading. I think almost everything that is worth having is out there or being grown out for distribution by professionals. Added to that number are hundreds of new varieties that are being bred by ordinary people. If I grew a hundred varieties a year I still couldn't keep up.
The reason for the USDA/GRIN is to protect varieties that might be needed for disease resistance, etc.
I can't see the backyard gardener wanting to grow some unknown, possibly bad tasting, and extremely rare tomato.
There are lots of programs tha are paid for by the public but are legally restricted. Send in a form and ask for some biotoxins, anthrax, or missiles and see whether they send you some.
LoreD