Mike,

Just replaced my muffler, heater control boxes (NOT exchangers) and main heater
pipe on my '78 T2.  Got my parts from Rocky Mountain Motorworks, their prices
are a LOT less scary than the dealer's (whose wouldn't be!).

I don't know if they stock Vanagon exhaust components, but you can check.
Their number is in the "Some_Parts_Suppliers" area of the VANAGON gopher
(point your client toward "halfdan.med.umn.edu").

Good Luck

Kurt