The M40A3 uses a 30 MOA base made by DD Ross for the USMC, but if I recall correctly he does not sell it unless he also machines your action to fit it.
The Badger Ord base which is close is the 306-06UX, but its a 20 MOA base and the overall profile is a little lower than the Ross base. Its pretty close but not exact.
There was a group buy for a clone of the Ross base a year or two ago here on the hide as well which is where I got mine from.