Just the AUG magazines unfortunately. I wish some manufacturer would make an A3 NATO!
Saw a video where a guy modded some PMAGs to fit but it means taking a big chunk out of the back and a portion of the front to replicate the AUG mags shape.
There are AUG mags by MAG on eHobby Asia still available at the moment. ~$40 IIRC. Worth bearing in mind they appear to be out of stock everywhere else (in the UK)
EDIT - sorry I just saw brotherwood linked the same ones -sorry didn't fully read whole post- thought they'd be available there as well, but yeah they're probably the best for the money.
I think I'll buy an AUG sometime as well. Even though I was just gonna go bog standard AR and pimp it up, but if I really want an awesome looking M4 I'll get a GBBR so it's especially satisfying and more unique + no battery limitations (both in terms of where it can go and size you can use) Speaking of customising etc AUGs are great to spray paint (cos of the huge stock / body that is one piece rather than separate receivers / handguard / stock if you catch my drift)