Jones Truck and Spring Repair, Inc in Columbus, Ohio installed a lift axle for us. They do a lot of them as they put them on their own trucks ( a fleet of sand and gravel trucks). They had many units in stock and I would not be surprised if they might have some used equipment.
They later added shocks to mine and solved the "bouncing" problem I was having.
The number in Columbus is 1-800-828-6769. The person I dealt with was JD.
Good Luck.