FYI update:
The air bladder is actually a Goodyear Super Cushion Mini Lobe Part number 1S3-013. These may be different on the H3. They are 3" air bladders. Looking at the catbase specs, some coaches use 4" bladders at some of these locations. I did not cross reference to your Firestone specification.
The regulator is a Williams Controls Part Number WM-279-E1. For those who are interested, there is a repair kit for these it is repair kit 114224 from Williams. Most other parts for these are available.