There is one sizable one with 3-4 counters at Armenia 2109, C1425 CABA, Argentina. And Yes, I went to ask at the counter and they confirmed they can only give out peso.
You may check the rate on western union website in the country of the origin of fund, along with the charges/processing time for different channel for transfer. Recent experience to share - This Tuesday, I tried to transfer from Hong Kong bank account and it took 1.5 days to become available for pickup. No handling charge and the rate was 108. I also tried using a credit card, cash become available for pick up in 2 min. Handling charge was USD2.5, rate was 108 as well. I read it should be counted as cash advance , but i prefunded my credit card and dont see any interest/cash adance charges so far on online banking.
One important things to remind - they only serve you on certain day based the last digit of DNI or passport number. Monday 0-1, Tuesday 2-3, and so on, I was refused to be served because i forget this rule.....