What you're looking for is not going to be "Shield specific"...it's either going to be for a double stack magazine (i.e., G17/19 magazine, FS M&P magazine, etc.) or it's going to be for a single stack magazine (that's the category the Shield magazine fits in).
I use the Blackhawk clip-on single mag (single stack) carrier. I'm wearing one now. It's plastic, not leather, and has a big tension spring in it to hold the magazine securely in place - it also has a full-length clip on the back.
Here it is: BLACKHAWK! Single Magazine Pouches | Bass Pro Shops
I'm not promoting Bass Pro Shop; in fact I don't like them...you can find these anywhere, it's just that Bass Pro's link had the best picture and description...I got mine for $19/ea at a local gun shop.