I'd call the information operator in El Paso, TX for the number of El Paso Saddlery and ask for their address and order their catalog. I'd get their Tom Threepersons design in basketweave stamping. It's also made plain or in floral carved. If you have a Gun Digest handy, the address and 'phone should be in the indices to manufacturers, suppliers, etc. in the back. I don't have time now to look it up. They also make a thumb-break model, and have a "pancake" style for concealed wear.
Or, find a dealer who carries Bianchi products and ask for their No 5 thumb-break. I think that Galco may have a similar model. Finally, look for these and similar older Safariland models at gun shows. At shows, expect to pay $10-40, depending on condition and who's selling it. Sometimes, U.S. military holsters turn up at shows or in, The Shotgun News. One guy mentioned Don Hume. They're good value and well made. In Miami, OK, as I recall. Get the catalog.
Determine how and why you'll wear the gun and select accordingly. If you have access to big gun shows, that may be the best deal. The M&P (M10) deserves a good holster.
Lone Star