I was visiting with another Yamaha enduro friend over the weekend. He has 3 IT models, 2 175's, and a 1976 IT 400, which is rebuilding. 
I noticed this very neat box of hardware, all separated into little compartments with bagged up bits. He said it had a complete set of hardware specifically for his 1976 IT400. They are put out by an outfit called "Specbolt". He was pretty excited about it, as all the small hardware on the bike he had was pretty grotty. 

So I looked it up on the web, and here is the site:      specbolt.com/

They seem to have a lot of different hardware, with a lot of it more-or-less aimed at Japanese bikes. They carry complete kits and engine kits, both zinc and nickel plated. (They seem to start around 1970, so my '68 wasn't there. ) Apparently they will look up your bike on a parts manual, and send you everything needed from that. My friend seemed to think his had everything.

Thought I would post this up in case it might be useful for others. 

(and for what it is worth also, I have gotten several pieces from Motodad on eBay, who carries some very specific Yamaha enduro hardware reproductions, which I have been pleased with).

I'd be lost without those SPECBOLT kits. I'm on my fourth one. I haven't seen one yet that is specific for the old Enduros, but even the kits for the later YZ models will have such an assortment that you will easily use them up. I have found creative uses for the special fasteners that were intended for the YZ plastics. But then again, I refurbish my bikes as opposed to doing an original restoration. So I am not so concerned with having the correct type of fasteners. I just like having nice fresh new fasteners. This one is my favorite.

specbolt.com/yamaha-vintage-yz-it-2-stroke-250pc-bolt-kit/