I had lots of drum brakes in the '70s. The only rear drums available were made for tandems, such as the French Atom tandem drums. Phil Wood made a jewel-like tandem drum that was too beautiful and unprotected from dirt to use off-road.
There were a lot more choices in front drums for klunkers. Now and then you could find a Union, which for my money was the best, or an old Schwinn drum, but it's almost sacrilege to use one up on an off-roader.
A popular source was a peculiar style of Schwinn 20" bike, the "Krate" series, that was banned for safety reasons, but had a front drum. Of course, it had only 28 holes, so you drilled four extras on each side to lace your 36-spoke rim. We destroyed lots of these now highly collectible bikes just for the brakes, because the brakes were actually pretty good, and had aluminum shells that cooled better than the steel brakes.
Easiest to come by in the '70s were Worksman front drums, made for industrial tricycles. They were ugly and cheap and weren't really made for intense downhill though. You wouldn't use one for a retro build.
Sturmey-Archer made two versions of front drums, a 70 mm and a 90 mm. They were beautiful, probably the most attractive of their ilk.
Obviously the 90 mm had more braking surface, but it had a unique drawback. In order to have a low flange on the side away from the drum, the spokes were not threaded through but hooked from the outside through a keyhole shaped hole, each of which held two spoke heads. If you flexed your wheel, you could pop all the spokes out of one side!
On a big ride in 1980 a rider did exactly that, and because I had built a lot of those wheels, I sat down on the trail and built his again.
Drum brakes have the same advantage that discs have, which is that you can trash your rim without affecting the braking, and I have certainly done that. Under sustained load they fade though. They're a lot heavier than discs, and if you are after performance, go with discs.