I bought a rebuilt hydro vac for my 450, also. The local parts rebuilder didn't have a kit, but his distributor in NC did.. The place in NC also had a rebuildable core in stock so he had them rebuild it and send the whole thing. It might depend on the exact hydrovac, but I wouldn't think they "don't exist in the wild anymore", there's too many of them out there.
Good luck and keep us posted. I'm about to go through the brakes on my 46 and I know I need a hydro vac, so any resource I can use, I'm all for it.
Scott
