20 round AR-15 mags at a decent price at Sportsman's Guide.

[DocGlenn]

The supply seems to be coming back slowly, but if you need some now, this might be an option.

http://www.sportsmansguide.com/net/...nal&utm_medium=email-flash&utm_campaign=f309p

 

[30SMK]

Out of stock!!!!
Supply trickles from time to time but will not be back for god knows how long.