I've ordered two different caliber magazines from S&W. 2 .22lr mags in Dec and 2 9mm Shield mags in January and am still waiting.
I did find a Shield mag on 44mag.com and got it in already but they are out of stock in the 10 rd you are looking for and the 17rd I'm looking for.
edit: It does look like there are quite a few on ebay. Might be worth checking it out.