Thanks Phred, but somehow I think my vet and Doc Mike went to to different schools. I told him he's a regular and he had just been in and all they said was "Well, we're usually understaffed on Saturdays and if he was just here then he's fine."
'Course that was the receptionist and I was so irate I didn't bother talking to the vet himself - probably wouldn't have been able to talk to him personally anyway with her on the phone.

I did get him in at a cat only clinic. Don't know if that will make a difference but at least they didn't say "we're booked" like everyone else I called. I did have the regular vet fax a copy of his most recent blood test, which was Oct 30th, just 3 weeks ago, so we'll see what they say. Saturday 12:30 is the appointment.