what coupler will match EZ Mate?

Kadee coupler heads are all to the same design and will all couple together and all couple equally well (or badly) to other couplers. Basically, all the couplers that look like Kadees should work with Kadees. There are a few oddballs, mostly scale couplings (Sargent engineering, ancient Devore, scale dummies) that don't come close to mating with a Kadee.
Some of the "clones" seem not to couple as well on curves.
Kadee do make a few odd sizes of HO coupling. There is the 58 "scale" coupling which is fully compatible, then some "old timer" smaller couplings that can be coupled to the full size ones, but may not do it automatically.