It's actually called "Soukenbicha". Not that it matters, because a Google search with that yielded no real leads either. You might just want to drop by a Japanese grocery in your area to see if they stock it.
Also, for the record, this bottled tea isn't really pure tea. It's a blend of many things, including barley, wheat, herbs, and grass-like plants. Oh, and it has some Pu-erh as well. At least, this is what the advertising jingle for Soukenbicha says it contains.
--crymad