This link goes right to them, Borg dually valves
Duallyvalve Kits for Class B or C - Sprinter Trucks
Every tire must be pulled, valve installed and remounted. Cost varies depending on your service area and tire shop doing the work. Maybe around $100 to install, perhaps more. Don't forget you will need to have each tire balanced again. It is tough to balance the inside rear tires with those long extenders - tough. Several folks have had a terrible ride post install of those valves, others no problem. Like other things it varies, tires good, out of round, was it riding smooth before the change, etc.
I have the steel wheels with crud covers. Some tie wrap them with stainless tie wraps, I use just the nylon tie wraps, no sharp edges, two per cover opposing each other. Not a worry for you with alum wheels. All you will have to do is keep em polished!