It's hard to find older shower door hardware. Any suggestions?

My house was built about '87 and the shower doors are metal-framed. I can't find a brand on them. I'd like to buy 4 of the plastic snap in guides for the bottom track. Also, I had to take off the towel rack because I put in a shelf tower right next to the shower and there's not enough clearance to open the door all the way with the towel rack in place. I'd like to find one with a lower profile that might fit behind the shelving. But it seems almost impossible to find replacement hardware for older doors. I can't afford to get all-new doors. Any ideas where to look?