On line you can order them from K&B www.modelengine.com
I wouldn't pinch off your exhaust yet if you ever intend to use a pump eventually. It should run fine on bench with stock pitts exhaust enough for you to dial in carb. Only pinch off a tube if you are not going to bother with a pump later when you fly. Otherwise, you are restricting your power potential. Pump or pinched exhaust, not both.