I use 0000 steel wool with a little bit of oil (3n1 or Mobil 1 - doesn't matter as long as it's a light machine oil). I put a couple drops of oil on the steel wool (small piece, torn off one end of the bigger pad) and lightly rub the rusty areas. Then wipe with the same oil rag I wipe my guns with after handling/cleaning.
I've noticed (for some reason) that I'm not having an issue with my pistol magazines (MecGar or CZ - made by MecGar I read hear) rusting.
I carry the spare in my pants pocket. I handle it putting it in the pocket, handle it pulling it out to set back on the top of the cabinet, repeat, repeat, repeat, 3 or 4 times a day. I keep looking at them and they are still looking good when I do wipe them down with the oily rag after a week or more of daily handling.
I don't know how badly your mags. rusted. The above process won't remove pits in the metal, just the surface rust.
Couple of pics if you haven't seen them. Rusty piece of shotgun barrel before and after the 0000 steel wool, 3n1 oil, light rubbing, wipe down with oily rag.
You can see a large rusty area on the right side of the barrel piece, near the tape.