I was digging around in a little hole-in-the-wall
used computer parts shop in Seattle, and ran across a small stash of Cherry G81 point-of-sale keyboards:
G81-8000LPCUS (two of these)
G81-7000LPCUS
G81-1901HSU
They're a bit dusty, but all of them seem to have a full complement of key caps (after I re-attached a stray) and no obvious damage. They have magnetic-card readers built in, but I didn't spot any evidence of the optional barcode readers.
He's selling them for a little under $20. Pretty pricey by his standards: he sold me a Kinesis Maxim -- an adjustable-split ergo board with rubber dome switches -- for $4.