I actually found some random caps that fit them in my Signature Plastics grab bag and I was also able to put a few SA key caps on there by sniping one of the arms with a wire cutter so it stretches.
these things are really easy to convert to USB with a teensy or other board and Hasu makes a native converter that works best.
seriously 2 resistors, a few wires, and a micro controller, this is a dirt cheap cool keyboard to add to a collection. tmk programming can be challenging, if you have a teensy you have to do it the long way instead of the GUI. but its worth it. It smells like the 80s and isn't a bad keyboard.