Lots of guys manufacture their on gaskets with much success, not sure I would make an exhaust gasket out of rubberized fiber though, but to each is own. The cart shouldn't smoke that much if any, if your cart is smoking its most likely your fuel to oil ratio, or your rings could be shot. If your look the proper exhaust gasket they are all over flebay, only $7.75 and that includes shipping. and most all cart part suppliers have them as well.
Good Luck
http://www.ebay.com/itm/Columbia-Par...77b17e&vxp=mtr