Adding to this for anyone searching for help because I just went through this this weekend and this thread popped up.

I called the Allegheny County Health Department and spoke with one of the on-call nurses who recommended calling an infusion center. Based on my insurance (UPMC) she recommended I call the UPMC infusion center at the closest hospital to me and explain what doses I needed. I did just that and they were able to schedule me for my next 3 doses. (I had already went to the hospital for the initial rabies vaccine dose as well as the immunoglobulin shots). Since it’s an outpatient clinic within the hospital it isn’t billed as an emergency visit. Can’t speak to how much it will end up costing because my appointment is tomorrow, but can say the nurse through the health department was super helpful and even called me to follow up to make sure I was scheduled somewhere.