I was intrigued by your mention of custom keycaps, so for the first time since I bought the keyboard I pulled off one of the caps to find a kind of usable fader still left there with a little red mark for the center. Now I'm googling for custom keycap options. So much for avoiding GAS.

Gear Acquisition Syndrome (GAS)

I don’t think there are any readily available keycaps for your Axiom because M-Audio used faders with an odd size of stem and probably made custom moulds for the ones you have.

What I meant is that used Axioms are usually missing keycaps.

But they can be found cheap and have many great features. Plus the keybed is ok’ish.