Air-Life is a company in Lansing, MI, and since my retirement is paid for by Michigan, I naturally advertise them.. Many RV dealers carry Air-Life, as does JC Whitney.. Or you can google for them.
I"m told Firestone air bags are a bit sturdier.. but I had Air lift (the one set I had) and no complaints.
I will be putting air lift on my motor home.. Some day (hopefully next summer)