How do I find blocked players?

There's no block list. You'll have to find out what their username is exactly so you can search it in the ally search box or try to find their clan and look through all 50 members (or however many) to find them if you can't...but since you don't know their name or clan, you'll have to wait until the devs finally decide to add a block list...maybe even make a feature request in game for that... (It has been requested before, but you requesting it can't hurt)