The only number I can find on it is on a brass tag attached to one of the bolts. That number is 378802.
That's the Bendix part number. You can search it on-line...
You really want and need the Hydrovac working. Modern cars stop way to fast and you need all the help you can get to stop your heavy truck.
Last time I called Precision they were one of the major Hydrovac rebuilders for companies like NAPA...you might reach out to them and see if they can help.
http://precisionrebuilders.com/Mike B

EDIT, here's White Post's info
https://whitepost.com/brake-sleeving-rebuilding-services/