Powder coating would be ideal but expensive and may take a few weeks. Alternatively, the Motip brand of rattlecan primers and finishes (available via Amazon and other retailers) are a good match for, for example, Target racks and stands, and have proven resilient in outdoor applications such as my old motorcycles.
Some of those screws and nuits have seen better days. Depending on how "original" you want to be, stainless or adonised black alternatives might be better. Boltbase are a quick, economic and relaiable postal supplier, either direct or again through Amazon.
This is a brilliant thread.