if you pony up enough $$ They will build you anything you want
the question is more likely is it worth the added cost??
I don't think any major company DOESN"T have a custom shop today
a new barrel in the aftermarket world is always an option too, NOT likely much cheaper
but is there if you HAVE to have the extra 2 inches!
gains of a 2 inch longer barrel, is what, 40-50 FPS, IF that??
so, keep that in mind here!