The store name is Key Whoss, and I love the sign on their outlet store (Discontinuous). There's a regular branch on Cabildo somewhere between Echeverria and Monroe and an outlet is on Juramento between Cabildo and Vuelta de Obligado.
Punto 1 seems to be popular, there's certainly quite a few, one on Cabildo near Monroe and one on Cabildo at Virrey del Pino, just outside the Jose Hernandez subte stop. Some of their stuff is decent quality but overpriced. If you know someone with a Club Nacion card (like me!) you can get a 20% discount.
Also on Cabildo near Monroe, I forget exactly where, is a small store called Fibrahumana. I bought some very nice quality things there and the owner is very sweet.
If you don't find what you are looking for....
Not to brag, but my dad just arrived today with some Athleta brand yoga pants I ordered on ebay for $25.00 US and they are AWESOME. PM me if you might want to do the same--I'm headed to the US from 11.16-11.29.
happy hunting!