The only ones I have seen lately have been in pawn shops. You might want to check around....quantities are REAL limited right now, and I don't seem them getting any better anytime soon. In fact, if I had the money, I'd be stocking up right now.
BTW, the last one I got (which is now broken beyond use due to my younger days of stupidity

) was $20 for a 30 rounder (they sell 'em as a 32 rdner., but will only feed properly with 30 rnds. or less in them).