I would be skeptical of a clay model because it is so impermanent. Fraser did indeed work in clay but he would have made a plaster cast of his clay model. The plaster is what he brought to Henri Weil in lower Manhattan who made galvanos from the plasters. Weil even silver plated some of these galvanos to give Fraser an idea of what the coin would look like in a silver color (as copper nickel). These galvanos were considered "trials" by numismatist Walter Breen who coined the term "electrotrial."

There are a number of these metal patterns in private hands (via a Joseph Lepczyk auction) that anyone with even a modicum of casting knowledge or working with clay could have made a clay model from one of these metal galvanos. The exhibitors would have to prove the provenance of that clay model back to Fraser to be meaningful.