I purchased a few from Cheaperthandirt.com quite a few months, if not a year ago. They don't have the 12 rounders in stock, but they appear to have 10 rounders in:
If you're lucky, they'll lose your order, send you a second one, then find your order and send you the first one. Extra mags are always welcome lol.
This website is out of stock, but allows backorders. They also have a decent price.
The S&W website also has the 10 rounders for sale, but no 12 rounders on the site anywhere. :?
Hope that helps.