First, welcome to GTU!
You'd be very lucky to find some odd tuner-post bushings (that's usually what they're called) lying around. Occasionally, especially in smaller shops, they have a few drawers or boxes of assorted leftover odds and ends, but you'll be lucky to find what you need.
While bushings do provide some protection from elongating the post-hole in the headstock, there isn't a great deal of wear and it's usually extremely slow, so "cosmetic purposes" is probably as big of a factor as anything. You can look around and try to be "creative" in what you might use as a substitute. Tiny nickel-plated washers that match the post-diameter might be substituted. They offer no protection for the hole-wear but they work for the cosmetics. I had an old Precision bass missing one bushing. Coincidentally an eyelet-stud (like you use to put a tie-down eyelet in a tarp or something) fit exactly and even matched the look of the bushings pretty closely. However it was brass, but a little silver-chrome paint and now you wouldn't even notice it under the strings unless you were really looking for it. Same with an old long-neck banjo I found in a yard sale for ten bucks. A pack of little eyelets from the hardware store for a dollar fit perfectly, as if they were made for it. They even pushed into the headstock holes snugly and fit the tuner-posts exactly.
One of my 12-strings when I bought it had a small piece of simple quarter-round wooden molding for a bridge/saddle. It actually sounded pretty good just with that on it. I eventually replaced it with a better and nicer looking one that I carved to fit it and the contour of the body more exactly (it was an arch-top with a trapeze-type string-holder). I bought a guitar once that used a section of threaded-bolt for a saddle. Ugly, but it worked for the previous owner. (I replaced that pretty quickly!) Another had a piece of plastic... hmmm... you know those little thick plastic name-tag pins you might see on like a store employee or something? It was a piece of that cut to fit into the bridge saddle-slot. It worked fine. (And that was on a Gibson!) I replaced it soon but it did work and no one would have even noticed it if they weren't looking really closely.
A little cosmetic work can make a twenty or fifty dollar guitar look like (actually become) a guitar worth hundreds of dollars without actual refinishing. (Which is something you want to avoid if at all possible. Re-finishing tends to lessen the value of an old guitar, especially the finer old "vintage" ones.) You can do a lot with a furniture scratch touch-up pen. Sometimes even a plain old felt-pen (in brown or black or whatever color is necessary) works wonders. Touch up the nicks and scratches with the appropriate colors. Often then going over the entire guitar with a product like Old English restorer (the kind that also has a mild stain mixed in) will work wonders. I wish I'd bothered to take "before and after" pictures on some of the old guitars I've put no more than ten or twenty dollars into for supplies and assorted "stuff" and then had a really beautiful looking and sounding instrument when I was done. (My daughter who plays once found an old electric 12-string sticking out of a trash-can once on garbage-day on her way to school. That was a really nasty looking p/o/s too.

No strings, no nut, no bridge (actually, it had one rusted-string holding down two pieces of broken pencil used for the nut and bridge.

). Twenty dollars and twenty work-hours later she had a pretty nice guitar that she was eventually given $500 trade-in value for when she bought a new Gibson several years later.
You can do a lot with a little if you look at it sort of creatively and are you're willing to put some time and effort into it. And there really is a great feeling when you've taken some total p.o.s guitar and, after some work, have a nice one that plays and sounds great and people compliment you on.
Anyway, I hope that gives you a few ideas and, again, welcome to GTU.