Hi Craig,
1. Should still be available NOS from Yamaha if you are quick
2. NLA but join us on the IT forum and a member there is making extremely high quality and durable fibreglass versions molded from NOS parts. They are excellent
. DC do replica's but are a poor fit.
3. See above
4. MCS I think do a copy, other wise wreckers or EBay
5. Headlight shell and glass are the same as TT Yamaha's just different colour, other wise wreckers or EBay
6. See 4 & 5 above
7. Speedo - good luck :'( good second hand ones are going for stupid prices. TT Yamaha should work with the correct bracket, Cable should still be available NOS.
8. NLA but as Tony said plenty of good replica's around on the net.
9. See above.
10. DG, Pro Form GMC?? or usually decent originals on EBay or the wreckers.
11. Wreckers or EBay, quite a few models will interchange.
12. See above.
Come on over to the IT forum (sas well as here), plenty of knowledgable members that will help you out. Generally IT's are not too bad to get bits for if you are fixing up a rider. If you are going down the NOS rebuild road then you will be in for a search for bits, but they are out there. NOS or even good original IT plastics are scarce and you will not find many who would part with good pieces. Most other parts can be had pretty easily especially out of America. '83-'85 was a decal update so parts will interchange no worries, 490's & 250's.
www.boats.net is a good resource for part numbers as you can click on it and it comes up with everything else it fits. As usual a different colour will be a different part number and will say it is different fit, so you will have to learn your parts a bit though, but I guess all the manufactures do that.
Adam