I have been working on an AK magazine adapter to accept AR-15 style magazines.  Although this is most beneficial for the 223 caliber AKs due to the large quanity of low cost magazines available.  However, C-Products makes AR-15 magazines in both Russian calibers: 7.62x39 and 5.45x39.  These magazines are relatively inexpensive (~$10-20) but are not as prevalent as the 223 caliber version.  The pictures below show three C-Products stainless steel magazines in the three calibers.