I've been snooping around and I can't see any Shield 9 mm mags for sale anywhere. They're not even listed on the S&W web site. I usually have at least 6 mags for each gun.
They were hard to get when the M&P line first came out too. Figured I'd wait awhile (I did order 2- 8 rounders from my LGS when I bought it) and not be in a rush. The price should come down when we have them coming out our ears like the FS M&P's did.