Closest to you is the Saturday and Sunday markets in Parque Centenario, and nearby in Parque de los Andes, both, more or less in Chacarita.
They are a mix of old and new, junk and collectibles- vinyl records, incense, funny clothes, garage sale stuff, shoe repair, you name it.
use this map to find which collective to take.
http://www.omnilineas.com.ar/buenos-aires/colectivos/
looks like the 141 to Parque Centenario, the 39 to the Parque de los andes. While at Parque de los andes, visit the organic food market at El Galpon, just a block or two away.
http://pickupthefork.com/2010/07/28/el-galpon-market-organico/
Recoleta, by the cemetery, is just contemporary crafts.
here is a list of some of em-
http://landingpadba.com/ferias-outdoor-markets-visit-buenos-aires/
also, you might want to read my post on neighborhoods- if I could just find the damn thing- think its in "Articles".