Amazon has one but it's the whole set (Filco accessory pack 1). I just got one and it came with whatever you see below (including a Filco keycap puller)...
Here's a short description of the contents:
"The first accessory pack from Filco contains:- 1 set of blue 'W', 'A', 'S' and 'D' keys, 1 set of red 'W', 'A', 'S' and 'D' keys, a red 'Filco' logo printed escape key, a black 'Filco' logo printed escape key, a beige 'Filco' logo printed escape key, a red 'ESC' printed escape key, 2 black blank Windows keys, and a Filco key puller. The keys are designed for Filco Majestouch and Tenkeyless keyboards with Cherry switches, these keys will however fit all Cherry MX switches (they are slightly taller than the standard keys on a G80-3000 but have the same slope/angle to the key tops.). Replacing the keys is easy, simply pull your old keys off with the key puller, and push your new keys on."
Edited by reaper~ - 3/22/12 at 10:44am