Over the course of both betas I thought I had all the armors sets because I had about a dozen and didn't see anymore after that. But at the very end of the second beta I suddenly got a new legendary boot with a skin I hadn't seen before so I realized there must be some more. I bought a bunch of gear from the obol merchant and got a few new ones and then made a bunch of legendaries with aspects to get some more. The armor sets are really beautiful in this game. Especially the Necromancer and Barbarian.