I have 1982 GPZ7501R. Its all original, (minus the Kerker Header, jets, and a high flow air cleaner), 21k miles, un-restored.
I use only OEM part suppliers as they have 80% of what I need. For the parts they no longer make, I can usually find them on eBay, after that its a junk yard. I only had to go to a junk yard once and that was for spares that I thought I might need in the future.
Pete in SA
1982 GPZ 750
2019 Z900RS Cafe
2011 HD SGC