Econohonda in Te Aroha have a massive stock of new and used Honda parts. They have a big pdf file on their website which you can browse if you know the part numbers for the things you need.

I wouldn't bother boring it out, as soon as you start to play with things like that reliability takes a nose dive and the bike gets dearer and dearer to run. If you want more performance i'd recommend getting an MC21. Information on running them is much easier to find and tuning parts and genuine spares are easier to get. Plus its a newer, better bike all round.

If gearbox fluid is going missing it may be getting pulled into the crank case past one of the crank seals. It also sounds like you've got knackered main bearings as RZRob1 says.

It sounds like you need a new crank, left and right side crank seals and fresh pistons, rings, wrist pins, circlips, small end bearings etc. I'm not sure exactly what you need because i dont know how different your engine is to the MC21 engine.
_________________
After years of moaning about immigrants now i am one...