There are three basic AKM magazines:
7.62x39 (by far the most common)
5.45x39 (AK-74, not as common)
5.56 NATO (fairly rare, and NOT the same as a 5.45 magazine)
The 5.45 and 5.56 magazines don't have as much curvature as the 7.62 mags, and they're slightly longer front-to-back; they won't fit into a 7.62 magwell.
The only other mags you're likely to find laying around are the Valmet / Galil / R4 style, which may be found in .308, 7.62x39, or .223. The latching lug at the front is located a bit higher than an AKM due to the "slant cut" shape of the receiver. *Some* people have reported success using AKM mags in Valmets and vice versa, but it's a "try it and see" thing. If you accidentally acquire any, they're easy to flog off to the Galil owners.
The Soviet stuff was pretty standardized, but over 3/4 of a century the foreign-made variants and copies diverged a bit.