Other Costar-based fullsized Cherry keyboards should, generally speaking, take your keycaps. The 37-keys should actually fit just about any Cherry board ever, but stuff like modifiers and whatnot can be a bit more unique (since some keyboards use funky Cherry-style stabilizers instead of the Costar ones in your Filco).
Beyond that, if you do get a board with a removable USB cable (for instance, the Rosewill RK-9000 series have them *and* are made in the same factory as the Filcos were, making them virtual clones of the Majestouch 1 line), please be sure to treat the connector with respect. If jarred constantly or yanked around, it might come loose inside from the soldering/wiring/circuitry it uses to communicate with the keyboard's controller.
Mind you, it's not exactly easy to do, but if you're careless or needlessly violent, you definitely can cripple a second keyboard.