NHMTG is making the straight bodied 20 rounders but it'll have a black plastic follower instead of the ultra reliable aluminum alloy follower. NHMTG is Circle Kay. (Circle Kay made/makes Colt)
The old 20s will serve you just fine as long as the feed lips aren't bent, no dents to the magazine body or rust on the spring. Also check out the floor plate retaining ears for any sign of bending or missing ears.
If you want to judge the history of use on a used 20 round magazine w/ an alloy follower- look for the presence and depth of a small dent in the follower itself which is formed by one of the locking lugs striking the follower on it's rearward travel after the last shot & before the action is locked by the bolt catch. The deeper the dent, the more miles it's had on it. Even w/ this dent present, a vast majority of the old 20s w/ alloy follower still have a lot of life left in em.
Refinishing the older 20s is easy to do. The original finish was very "soft" & transferred/rubbed off very easily and is thus, IMHO, a poor indication of actual useage as the magazines were commonly carried in 7 pocket bandoleers. I suspect carrying them in this method could easily rub the finish off after many miles humping the bush while the magazines may have either seen limited use to no use at all.
Sly