if its for exhaust try Inconel instead. Its a high grade stainless impervious to heat. The biggest plus is that you dont have to weld it in a perfect vacuum like titanium and only have to backpurge it like regular stainless. it puddles funny and is hard to weld but is not too much of a problem for an experienced TIG guy.

as far as titanium goes you may want to try Dynamet off 49th street

dynamet loc: Tampa, FL - Google Maps