It would be difficult to find one, the Aurum blades I have are prototypes but they are really Aurum prototypes on Buck blades not Buck prototypes as they were different companies.
There must surely have been over a million buck 110s made now and many 112s also, to find an original prototype of the very first buck 110 or 112 would be exceedingly difficult, Companies normally keep them in there own secret stash.
Photosamples are a little easier to find often marked with multiple zeros, I dont know if same applies with Buck knives. Although these also are often held in the companys own stock.
There is a little debate about what constitutes a prototype, often several were made of a particular type before final production, sometimes they dont go into regular production and cost to make single peice can be very high for example I have a few of these small hand size Aurum etched plaques made at a cost of several hundred dollars each but they never went into regular production. The cost of producing these would normally be absorbed into the profit made should they go into production.