Pistol hasn't been out long, might not be easy to find mags. I'd try gunmagwarehouse, cdnn, Brownells, MidwayUSA, and maybe GregCotes. Failing that you could also call S&W and see if you can buy them direct.
If the design is comparable to past M&Ps (which I'm almost certain it is), you can use mags from the full-size M&P at the range or as carry reloads. The base will stick out but they will fit and function properly.
I realize you're in CO and have to bear that state's 15rd limit. S&W actually sells a 15rd full-size M&P9 magazine, although I understand that they're hard to find at a significant discount, and I could understand not wanting to be stuck with oversized same-capacity mags if you don't have a full-size pistol to use them in. If this is the your issue, TunnelRat's answer sums up the situation.
If the design is comparable to past M&Ps (which I'm almost certain it is), you can use mags from the full-size M&P at the range or as carry reloads. The base will stick out but they will fit and function properly.
We'll see... I've heard conflicting reports on whether the rebate applies to this gun. It doesn't say so on the website and the official rules exclude it by their definition.... however calling S&W CS, the rep said it was included... so who knows. I tried to fill out the form online and it said they couldn't locate the serial number provided in their system and to mail in the rebate form... so I'm doing that this afternoon.
Hopefully I get the stuff, but I won't be surprised if I do not.
At any rate, I'm REALLY happy with the gun. It's perfect - after a little bit of muting to the grip texture. Though I'll take a grip that's too aggressive over one that's too slippery any day. I can soften up a grip that's too aggressive easily. It's more difficult to make a smooth grip aggressive unless you add tape or destroy your resale value by stippling.