assuming you have argentine medical insurance which I would suggest to anyone here for more than 3 months.
Go to any local clinic get an appointment with a clinician and ask him to write out a prescription.
Then you can either get the shot in their vaccine centre or go to a good hospital where most have vaccine posts.
If anyone would like a referral to a good health insurer do post me. I know a wonderful insurance rep (Medicus) who is happy to arrange short term insurance. Probably costing around US$50 a month which includes dentistry. I often use this for student clients of my husband who come here to play polo which often ends in falls and breaks. It also gives you cover for up to two months abroad, which is very useful if travelling around south america.
It is true however that some vaccines are not covered by insurance