There's a load of them for cheap on eBay.
They're the same as the XT Model F, except with no obvious way to interface them with a modern PC.
... and, depending on which one you end up with, they can be _much_ harder to interface with a PC - assuming you are coding up a custom microcontroller firmware for it. If not... well, even kbdbabel din' crib up a driver for these, so porting from kurt's assembly won't even help.

Bhtooefr has one which is sort of parallel read, and I have one that is not even that: It has no controller, and requires the terminal to drive the scanning via parallel writes.
XT runs a simpler version of the PS2 protocol, with just one message, a couple've signals that take over their wires entirely, and it is timed a little different, and triggered on the other edge.
dfj