Turns out the sculpts were by Ron Spicer, the artist who designed the spaceships for the game and drew the illustrations in the Observer's Directory & Identification Manual. This publication, in turn, had drawing of each of the five races. I'm guessing the pictures in the Manual came from or served as his concept sketches for the figs.
Judging from that long-ago auction, and the fact that I hadn't seen them since, I figured these models were long out of production. I was pleased, then, to find at least some of them still available.
Perth Pewter evidently took up the mantle (or was spun off) from Superior and kept casting the 100mm figures, as well as versions of some of the larger Starfleet Wars ships, for the collectables market. I didn't find any Starfleet Wars merchandise on Perth Pewter's website, but Armik's Fine Collectables still has some in stock.