That might be an American Classic but the head does not look like the two American Classic posts I have. I bought a ti seatpost that was almost an American Classic clone in the late eighties. I believe it was made by a company in Arizona with a very brief existence. Like yours, my clamp broke but worse. I was able to replace the clamp piece with one from an American Classic though it did not fit perfectly. I think I had to do a little modification to it.
Brent