There are two types of IUDs -- copper IUDs and the Mirena (plastic essentially but with a low hormone dosage as well). Copper IUDs are for 2 years and I've heard varying reports... Mirena IUDs are for 5 years. Before you can consider having an IUD you will have to go to a gynecologist to make sure your cervix is of ample diameter for insertion (if you've had a child, you'll be fine, if you haven't, an IUD may end up not being the right option for you)
When you meet with your gynecologist you will be able to discuss the pros and cons of the two IUDs... (by the way -- DIU here... devicio intra uteral or something like that). Mirena's are known here but not seen often because of the expense. I don't think the Mirena is covered by low-level obra social, and I'm not even sure if the copper ones are. Mirena is pretty expensive -- it's $300 in Canada, more in the States, so probably bet on about $400 USD here.
The gynecologist will give you a prescription for the IUD, you'll have to go to a pharmacy for purchase, if they don't have the one you order in stock it may take a few days, and then you have to return to your gynecologist for insertion.
My gynecologist was familiar with Mirena but she told me you just don't see it in Argentina, but really I don't think the insertion technique for a Copper IUD vs Mirena can be that much different.
My gynecologist is Dra Claudia Rey, she's on Cabildo, she's with OSDE, she speaks english, but I was actually looking for another one for ages just because she specialises more in menopause (I'm 33) and more than anything because when I went for my appointment at 9am I didn't even get in until 1pm and I can't be bothered to waste 4 hours for a doctor's appointment!
My friend goes to Dra Liliana Voto. Her clinic deals more with Maternal Fetal Medicine but she also has a gynecology clinic. However, I called them the other day and despite being listed as taking OSDE 210 the woman on the phone informed me that they no longer work with that level of obra social and that a consultation would cost 300 pesos! Forget it!
Anyway so sounds like your first step is to find a gynecologist -- if you're with OSDE I know their book lists a bunch of different ones and the languages they speak. At 210, there's not a lot of women gynes... I prefer going to a women so I'm going to suck it up and wait hours at the office of mine...