Most of my enlarging lenses came with caps. This includes my EL-Nikkors, Minolta Rokkors, Rodagons and even my old Enlarging Ektars. All bought used. If you're buying used lenses, the caps were probably lost or kept by the original owner.
Guess I'm really unlucky then. Only a few Nikkors have front caps - Never seen rear caps for any lens.