I don't think there are too many KC-135E models flying anymore. I schedule 3-7 AAR sorties every week as part of the OCU here and we use all units - active, guard, & reserve. I haven't seen a KC-135E in well over a year...I'm not about to say they're all gone, as I don't have that bit of info, but I would at least put them on the endangered species list...
IIRC, my contact list for their scheduling, ops, & CP doesn't have a single KC-135E unit listed (but I'm at home w/o my list & make no claims as to its completeness as a comprehensive tanker listing, perhaps only half the country as we're out West - will try to remember to look tomorrow). I do recall having AAR cancelled over a couple of periods last year as a couple of the units were converting from E-model to R-model - these were primarily ANG units.