ive been digging around for this kinda stuff for years, and gotten nowhere.
i think its all custom made pretty much.
you might want to find a plexiglass cutter or a laser engraver nearby and see if he has some thick plexi in stock and see if he can cut the feet out for you.
i have a friend here who runs a shop, and while the cutting is a little on the expensive side, i cant argue with the results. generally most shops have a 1-2 day turnaround. i would imagine maybe 10$ (6 gbp?) for the feet.
chris