Good old Stove Enamel would be a good choice, but sadly this process has gone from a common industrial finish, more often "enamellers" are now Powder Coaters. Silver Powder Coating works well on sports car wire wheels, but of course exhaust pipes get hot, silencers not so much. Whether the coating could stand the ferocious furnace temperatures the way you ride..... Back then Silver Hammerite kept the rust at bay, and looked good from afar, far from good close up. Stove and Barbecue paint, high temperature but restricted to black. Silver Exhaust Paint looks a cheap and cheerful fix. Galvanising prevents rust, but I doubt the finish and internals would be to your liking after a bath in molten zinc. Any Chromer of repute would load the price to scare you away rather than put your unknown bits in any of the baths.
I'd give them a dose of WD after each ride to keep the rust at bay and look for something better.....then sell them to another like minded enthusiast. Any professional finishing will cost more than they are worth, unless it can be done by the informal arrangements common in most industrial settings. Bergs will know what I mean, a fine example to us all.
Swarfy.
Additional. Hylomar used Cellulose Thinners as a solvent, so old castings can be cleaned off if you have some to hand. "Belco from Halfords" No chance these days. Red Hermetite used alcohol as solvent, good old fashioned meths back in the day was the cleaner up of choice. Don't see it now.
