The Honda Rebel is a bit of a heavy vibration bike.
I used to lose engine side cover bolts on the Rebel practically every trip. I lost many of them, and replaced them with whatever the hardware store had when I was concerned about it. Really, though, you can get away with missing a couple here and there. It’s important to have as many as possible though to keep a good gasket seal.
Valve cover bolts are even more important. That’s one place you really want to have a good seal. The threads on that one are a little different, so you’d probably have to go to your local shop to get a new one, I doubt you’ll find it at the Home Depot.
I once lost a sidekick bolt between Flint and Detroit. I’ve got no idea where it went. Either way, what my solution was involved taking an engine side cover bolt that was a bit longer, and wrapping that in place with a bunch of electrical tape to hold it steady. It made it home just fine, thankfully.
There’s many more nuts, bolts, and fasteners on the bike of course, but those don’t often come off as easy.
My solution to most of these issues was keeping a bottle of blue Loctite with me at all times. I blue-d up every set of threads that went into that bike because I was tired of losing everything. It gets expensive!
My point is that you can find cheap replacements just about anywhere for the little stuff, but if you want to do quality and be able to torque it down, go with what should be there, or something better.