If you're talking the jet screw holder,teflon tape is my old standby for that sort of problem. Handy Bikes has anything you need for that.
Head gasket,you can use a piece of copper or aluminum flashing from Home Building supply. Base gasket,you can use the gasket material from an Auto Parts place unless it's the light colored paper. The darker stuff is better.
If you use too thick a piece of either,it will drop your compression though. dobn-ohio