What's it for? If it's a one-off, you may be stuck having to machine it to size or substitute another size. If it's a big quantity, you can extrude any size, but the tooling will be expensive and I don't know if you can do wall that thin. That wall thickness will probably be formed and welded ... and you could always fabricate that yourself from sheet, too.
this is where my company buys all the raw materials for our aircrafts. they have several different alloys. I didn't see anything in the size you were asking, but it you call, they might be able to do a special order.