I believe I saw a couple of the blued ones hanging on the wall at Wade's Gun Shop in Bellevue, WA. (425) 649-5995.
Good luck finding stainless editions.
If you know someone who's good with their hands, have them cut down a S&W model 39 magazine, blue or stainless, and weld or braze the floorplate back on. Cut the magazine coils only enough to allow six rounds to be inserted, such that the filled mag can be locked into the gun.
For some "grip sensitive" folks, leave the spring at a length where only 5 rounds can be inserted (allowing the mag to be locked into the gun). This will provide for better holding power. That is, holding the next round to be fed in place during the (rather fiece) Pocket 9 recoil cycle.