When I checked Midway the other day, the CS9 mags were out-of-stock, but could be back-ordered ... while the 3913/908 factory mags were now listed as Discontinued.
When I called the S&W factory (to order something else, as an armorer), I was told that they didn't have any 3913 magazines in inventory, and the person with whom I was speaking had no idea if they were going to be available in the future.
Now, most of the people I used to talk to at the factory have since retired, so I don't have many remaining contacts who could check higher up the food chain anymore. It wouldn't be the first time I was told something wasn't going to be reordered for 3rd gen guns, only to have it later appear for a vendor order, so time will tell.
In the meantime, if you want to enjoy a bit of sticker shock, try browsing for 3913 mags on ebay. Some folks apparently think theirs are made of Gold Pressed Latinum (STTNG reference

).
At least some places, like Midway, are still carrying the parts to repair/rebuild the 7 & 8rd single stack 9mm S&W 3rd gen mags.