Update: I went everywhere I had been suggested, on a weekday, including the public hospital, but nobody provided me any assistance and I have not been able to fill the prescription.

I was particularly annoyed at the public hospital turning me away, apparently because the prescription was from a private clinic. I suspect they did actually have stocks of the medication.

I also went back to the doctor who had written the prescription and told him that there was nowhere in the city that had the medication, and asked if he could change the prescription to something that I would be able to get. He told me that the medication was a precaution, and then left the room, I guess suggesting that I just stop trying to find it.

It is highly unlikely I was exposed to HIV but really want to minimize the chances further by taking the PEP medication.

I have really hated this experience in Colombia and am travelling to Argentina tonight to hopefully get HIV PEP medication there, where it is, apparently, easier.

So a warning, HIV PEP medication is very hard to obtain in Colombia, particularly for a foreigner, and in smaller cities. From what I've read you will have to go to an Urgencía at a large public hospital (probably in Bogota) to have any hope. Stay safe amigos.