Two letter .Infos are notorious for showing as available. They do not exist.
But there are a number of obscure country code extensions that have two letter names available to register. .LA, .VC and .HN come to mind, there may be as many as a dozen or two out there. I own several LL.LA's. Not sure how to evaluate them.
Many (not all) REGISTRARS have software that will not let you buy two letter names even when they really do exist. I spoke to someone at Godaddy about that a while ago, he knew about the problem but the market for them was so small that he didn't seem to care.
Now, at my new host I find that CPanel gives me a polite note: "We are sorry, but we believe a domain name must have at least six characters."
Utterly unbelievable!