Is above a U.S. size 8 really considered plus size these days? Yikes! For some reason, that makes me want to eat chocolate.
I'm more or less a size 6/8, and I used to have a huge problem finding clothes that fit in Argentina...I would always end up with a saleslady poking her head in the dressing room and then screaming MAS GRANDE out to her assistants. (Fun!). I think the mid level quality stores that aren't too trendy are your best bet...Portsaid, Chocolate, Kill, Awada. They usually have 44s, even sometimes a 46, which I think is akin to US 10. Those shops are everywhere, so I would go to Alto Palermo or Paseo Alcorta for the biggest selection.