SQLit, Reed, Backlash, Luke, and as always Colbyt, thanks for the URLs.
The "v tracks" seem to be the oldest type of roller; they are neither
round nor like a flat tire. The only way I can describe them is like a
tire that comes to a point, literally a "V" rather than a "U."

Anyhoo, I'll look up each of the catalog/sites you all offered and hope
for the best, 'cause springing for upward of $100 to replace aluminum
plates just because of these tiny rollers gets me sick to the stomach.