Many times its cheaper to replace the whole door than look for that part.
However if you have more time than money.
Contact a bathroom remodeler in your area. And ask him/her to call you when they are tearing out a set of these doors.
Offer him 5 bucks for the call and tell them you will haul them away(a big plus)
Be prepared for some soap scum covered parts but you may walk away with a full replacement set of parts.
What you don't use you can sell on ebay.