I'm glad you found the parts. But about aftermarket parts. I have had decent luck with aftermarket parts made for a specific application. I have a number of aftermarket parts on my Sportster. But I would never use parts from a hardware store. These are not designed for motorcycle use, may not fit properly, may not be made out of the right material, and a number of other problems. On my Sportster the stock vacuum petcock was leaking, and I did not want another vacuum petcock, because I like to be able to drain the tank. So I bought an aftermarket Pingle petcock from J&P cycles and it works just fine.
And yes, in many cases with old or rare bikes, like the Rebel 450, the parts are no longer available, and you have to improvise. I understand people are making their own cylinder base gaskets for these bikes. But using home made or non bike specific parts requires quite a bit more skill and a good understanding of how things work than simply bolting together stock parts. I have fabricated a lot of vehicle parts, but I am a professional mechanic with 36 years experience, and have built a number of hot rods and race cars. So far I have never had anything fail that caused a safety issue. You need to have more than a casual interest in this sort of thing to get it right. Right here on this site I have seen a number of bikes built buy people who had no idea what they were doing, and were rolling death traps. I can only hope that nobody died on them.
There used to be a guy on this forum named Henry Inva, who definitely knew what he was doing. Does anyone know what happened to him?