For exhaust pipes, look for one that has a 1 3/4" or 1 1/2" diameter with thick walled construction. The larger diameter will help the sound tone. The thicker walls will help insulate the heat, help it to sound quieter, and it will weld better.
My pick is Vegas Carts. They will sell you an unfinished builder kit that comes with the pipe in multiple sections with bends etc, comes with nice thick flanges. It can be cut easily with a bandsaw or even a recip. Welding with a standard 120v flux core welder is super easy. Or, just tack it together and take it to a muffler shop to be fully welded. Just make sure they spread the welds out to reduce heat warping.
Vegas Carts Kit:
this one is for a V twin, but they will make a kit for your clone.
https://vegascarts.com/collections/y...12399520448556
this one is fully welded for an EZGO with a clone engine
https://vegascarts.com/collections/e...wap-no-muffler