Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
What sort of speed are you looking at for a top end on the gauge? Lots of warbirds had ASI's calibrated in MPH but they may go too high for your needs. On the other side of that coin a Tiger Moth gauge may not read high enough.
Auster Autocrat, top end 200 mph, no redline. FSNorthwest Stinson, top end 200 mph, 170 mph redline. Both are round gauges with black background.