The Button Box in Amherst, Massachusetts, has a good selection of new and used squeezeboxes. They are manufacturing very nice mid-priced Anglo and English concertinas, too. You can find them on line.
I've been working on making my Anglo sound more like an English, as treewind suggests. It's fun and I think I'm actually growing new brain cells as a result of the concentration. The technique I'm after is the Irish style of playing -- "out of the rows" I think they call it. For example, playing the G major or C major scales without changing bellows direction (I have a C/G box). But I dearly love the punch I get from the old in-out in-out, playing chanteys and such. And it's more aerobic, too.