I search the air Springs for numbers. They are there, but then you need to measure the plates.
I then call frightliner. They gave me the pn. I searched the internet. Frightliner 20 miles from my house had lowest cost and their deliverey person delivered to the my door for free.
I had a frame and spring shop install the air Springs. Out the door it was $400.
Art & Joyce
35' DP Endeavor being pushed by a Kia Soul