Exhaust recommendations

With out seeing pictures its hard to tell on your routing of pipes but Im sure you can find all the pieces you need here. Air Flow Systems Unless you need some factory squished pipes then unfortunately probably need to go to the dealer.

 

Freightliner dealership in Phoenix almost always has the lowest prices, no matter what truck you drive.
I buy most of my generic parts there.

 

For something like that, I would call around to local parts shops & dealers. Going out of route in the big truck or paying and having to wait for something to be shipped usually isn't worth what little you might save elsewhere, IMO.