Pirelli has a new 2.50-12 out, as does Kenda. Dunlop's supposed to have 756's and 773's out this spring. As for Shinko offering one or plans to, I was told "no" and "I don't know". I personally like Michelin's MS-2 a lot and use them on just about everything now. But two of the guys at the shop just changed to those new Pirelli's and said they work really well in front.
We have had the Pirellis for a bit and now have the kendas as well as the tried and true Michelin. I also have a couple Cheng shin laying around and ONE Dunlop. They have had them out for almost a year on the pro mini bike amatuer national circuit. But you could not purchase one... I happend to get one.