S&W is having a very hard time keeping up with the demand for the M&P pistols. The demand has been so great that they're still having a hard time getting the parts, including magazines.
I suspect the virtually unceasing demand for the guns caught them by surprise.
I order mine directly from the factory, and I've had to wait (even as a LE armorer).
Sub Club #9; .40 S&W Club #1953; S&W Club #3913
Retired LE - firearms instructor/armorer