Rumor on the FN forum is that they're redesigning them due to the new "FNX45." I'd imagine it's probably true because magazine problems are one of the very few complaints about FNP/X guns. I own 5 and did have one bad magazine out of the 15. FN fixed it for free of course...
I've been looking for some spare mags for my Tactical. Couldn't find 15rd anywhere but I did find some 14rd here - http://www.hinterlandoutfitters.com. I bought three, they were like $50 a piece with shipping but no one else has any. I just need them for back ups and range work so I'm not worried about them being down one round. Check them out, they may have some more.