No offense, but.....
You want What?!?, for How Much?!?
Seriously, though.
Around here, you can get 5" pretty reasonable, because all the bullhaulers, and grainhaulers want to go 6" or bigger. That's how I got the 5" for The PackRat Wrecker. A bullhauler buddy of mine put 6" straights on his flattop. I got the stacks, mufflers, elbows & y-pipe, just for hauling it out of his yard. I cratered the mufflers, saving the stacks & elbows, and traded the y-pipe to another buddy, for a future favor.
Finding cheap 6"+.....good luck, man.