You have to measure the diameter of the exhaust pipe and use the same size pipe, elbow, and gate valve.
asmskimmer.com has kits, but I really wouldn't recommend this seller from personal experience. Go there and see the picture of what the is included in the kit and see how simple it is. The most expensive part is the gate valve, which should be $15-20 if in the 1" or 1-1/4" size. Try USPlastic for the gate valve.