I dont know if you'd find any Helicoils to fit your jets thread pitch/size but you could check around.
I was thinking you might be able to find a new main Jet with a bit larger outer thread size, then tap yer carb out to fit it. If the new Jet was sized too rich, you could just solder up its orifice and then re-drill it out as necessary to correctly jet your engine.
If your carbs other stripped threads had enough meat around the holes, you could probably tap these out to the next larger size too.