It may be a pain, but you could always make sure they fit, make any modifications, then send them off to Jet Hot for coating. I bought a used exhaust system for my old motorcycle that had some minor crash damage. I repaired it, made sure everything fit right, then sent it off to Jet Hot.
As far as headers go for the Vette, I bought some VERY lightly used (maybe not even used at all and just stored in a garage) Hooker Competition headers off ebay years ago for my Vette. I think I got them for $69. At the time I was planning on running a tall deck 427, so header mods were necessary, so a cheap set made sense. I never finished the install on the big block, but did mock them up in the chassis. They actually fit pretty well considering the 0.400" taller deck height. 2" primary and 3" collector, so they are older Hooker Comp headers, not Super Comps. The current plan is to go back with a small block so the Hookers will get mothballed along with the big block for a later date and/or project.
In conclusion, see what you can find on ebay, fit them up and then go for Jet Hot. Unless you go for block huggers, long tubes rarely fit without some massaging into place.
-Red 77