As far as I know, in the States they are available only at Phyto universe in NYC (where by chance I happened to stop by this weekend). A few stores do carry a couple of prepackaged Caron extraits (I've seen some in Boston and here in DC). I think they go for about $200 for 15ml or $250 for 20ml in the spray bottle. Which is the usual price for extraits (similar to Chanel and Guerlains).
The problem is that, as you've probably seen from our endless discussions, opinions vary on whether they're still worth it or not. Most have been reformulated in one way or another, despite Fraysse's protestations. Regrettably, I have not smelled the old marvels, so I cannot compare, but it's true that some of them fail in the drydown (Tabac Blond being an example).
If you like something in edt/edp, though, it's certainly going to be better in extrait. Caron's extraits are much richer than the corresponding edt, if it exist.
I own Acaciosa (dirty sweet jasmine-orange blossom) and En Avion (orange blossom leather), and like them a lot, though I suspect that their earlier incarnations might have been more dark, leathery, and musky.
Our own Larimar is a Caron expert (and Caron lover) so he'll be able to chime in soon.