Much of the stuff from the usual suppliers is not good quality. There are still a few parts made in the UK that are decent, but much of the stuff comes from India, Indonesia, and I suppose China, and it's made by people who are well removed from the cars and see the parts just as a thing described by a drawing, which may or may not be accurate.
Your options are to buy the stuff and try to make it work, or fix it; buy used original parts from eBay, Craigslist, or other such places; make them yourself when you can; or buy from a few independent suppliers (like Peter) who supply good stuff. They're out there. Peter, for example, will rebuild your shocks better than original. I once bought a set of axles for my bugeye from a guy who buys old axles, the strongest ones made, then crack-checks them and hardens the splines further. And so on.
The short story is that you're no longer in the world where you can just go to a single source like Autozone and get whatever you want. Developing the skill of finding parts is instead part of the whole process of owning these cars; eventually you learn where to get things, what your options are. Some would say it's part of the fun, but I guess you need a sufficiently profound concept of fun.
Good luck--