Well, that's certainly not very good news. It has not been very many years since they quit making that lathe. I had a similar experience several years ago when I needed a part for a stationary planer -- a fairly expensive machine and they no longer supported that machine either.
I have a box of Delta pulley parts, but I do not think that I have a usable fixed half of the pulley for the motor. I will check anyway. One of the problems with getting replacement pulleys is that they need to be purchased as a matched set of the two halves -- otherwise the fingers of the two halves probably won't mate together correctly. This is because the keyway slot is machined after two halves are matched together. Even the slightest mismatch caused by the variation in position of the keyway slot will lead to an interference problem. You might double check with Delta to see if they have a pulley set for the motor if you have not already asked about it.
The other option would be to check with companies that have far better customer support such as Jet or possibly Grizzly. First, determine whether any of their models with Reeves drives have similar sized motor pulleys. They do not need to be exactly the same size as long as the pulley is large enough so that the belt does not jump out of the groove and has about the same range of travel on the motor shaft. Jet had a 14 inch model that was a close competitor to the Delta except that the motor faced the other direction and the fixed half of the pulley was closest to the motor face while the moving half and spring were near the end of the motor shaft. The Jet 1236 might also have a motor pulley similar to the Delta. Grizzly also had some Reeves VS models. You might check their archives for user manuals with exploded parts diagrams. There is a slim possibility of finding an aftermarket supplier, but I would not build up my hopes too much.
A last resort would be to find a set of fixed cone pulleys that would give you a decent speed range. The one problem there is finding a pulley set where one pulley has a 5/8" bore and the other half has a 24mm (or 22mm if a rev. A model) bore.
A more difficult solution given that the headstock slides and rotates is to add a jackshaft and have a 1:1 drive between it and the spindle and then the stepped cone pulleys could be on the motor and jackshaft. The real tough nut to crack here is where and how to mount a jackshaft without loosing the ability to move the headstock.
BTW, the reason for the pulley cracking from the hub is because the setscrews have been overtightened. DAMHIKT 😀 If the setscrews are not tight enough the pulley will loosen and move around -- if they are too tight the soft die-cast zinc pulleys will crack. The difference between not tight enough and too tight is a very fine line.
