If you want to keep them dry and extremely thoroughly retained, you can squeeze 25rd surefires into the very cheap but decent quality milsurp East German "Rain Pattern" AK 4x mag pouches. CSSpec 20rd mags fit in far more easily, though.
Made for x39 30rd mags, but they're rectangular pockets made for the very nonrectangular curvy x39 30rd mags, so they wind up suitably sized for battle rifle mags.