I wouldn't have replied to this post, since you are looking for a US distributor, except for the previous post about Stone Audio.
I also purchased a Headmaster from Stone Audio. It took four months and four overseas calls (Stone dosen't seem to like responding to e-mails) to get it. Stone seems to be all over the place about filling orders, from 3 days to four months. If you have to order from them, (and you might have to, they seem to be the one of the companies that can really deliver on the Headmaster) I'm sure you'll get your amp, it just might take a while. Is the amp worth it? Yes, but I was beginning to wonder at about the three month mark.
Somebody else replied to a post about the Headmaster and Stone Audio (I can't seem to find it right now) with a three word post of "Proceed with caution". Good advice.