Blackhawk told me personally (well, e-mailed me at least) that the M&P will fit holsters designed for the Glock 20/21. Of course, that could just be for their balckhawk line, and not for other manufacturer's holsters (which may be molded differently).
Galco specifically lists an M&P holster (Fletch model). However, if you cross-reference their model number (FL276/FL277) you will find that it is the same model as designated for the Sigma 9F & 40F.
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