Kelderman Airride sells complete kits for a lot of 4 x 4 stuff. If you want to build your own kit, you can check the pdf instructions online for all of their kits.They list what bags they use in the kits in all of the instructions. I was able to cross reference what I needed and find some stuff on
www.truckspring.com. The majority of the bigger stuff is going to be firestone components and any big rig shop should be able to get them for you if you know the part #s.