Actually, you might want to head to the police station that is local to where you are living. I had to do this today, and I went to the 7a comisaría and they told me they couldnt do it, that the 8a comisaría had to do it because my residence fell in the jurisdiction of the 8a. Just a suggestion, since they might give you trouble for that. You can type in google comisarias en buenos aires and you should get lists of which comisaria corresponds to which.
As was already said, you´re in for a fun experience. Or a ¨fun¨ experience.
Anyone who´s done this before: how long did it take the FBI to get your record to you here in Bs As? And what did you do about the lack of apostille problem (assuming this is for migraciones here). Thanks!!