Just like everything else on a go kart, you can find pedals at a junk yard. Pull them off a riding lawn mower. They'll probably let you have them for a dollar or two each.
a $4 piece of 3/8in rod can make 2 or 3 pedals. I cant really explain it that well, but mine are shaped just like racing kart pedals. There are 3 bends in each pedal. i didnt weld a bolt, instead I bent it in a way so the pedal would be 1 piece and drilled a hole for a hitch pin to keep the pedal on. I can get a pic later.