People don't want to pay $40 for a 17-round mag straight from S&W, so they hover over the 3rd party sites waiting for things to be in stock...then they buy them up. Same thing happened to me. I was watching G&R Tactical ($25 for a 9mm 17-round!), and they were out of stock, out of stock, out of stock, out of stock...and then one day they had them.

Hang in there and keep looking...or go to S&W and pay twice as much.