Do they have decorations at Mercado de las Pulgas or just furniture?
They have TONS of stuff other than furniture.
If you are looking for art I suggest you go to Esmeralda 600. Close to the corner there is a "galleria" of shops, mostly selling art. I haven't been there in over five years, but some of the same vendors should still be there.
First go down the hallway and on the right side, just before the space "opens up" in the back, look for a small space that should be full of art (if the seller I know is still there). His name is Gustavo Piedras and he is a big man in his 50's. His son Paublo was also working there in 2010.
Tell them Steve (the American who used to live on Arenales in Recoleta) sent you.
If you can't find them, look on the other side of the "open space" for a man with white hair. He has/had serveral "locales" in the galleria. His name is Celestino. He won't recognize my name so if Gustavo and Pablo aren't there anymore, just tell him you know someone who recommend them. If Celestion is still there he should have a lot of paintings for sale at competetive prices. I suggest you shop arround before you buy and search mercado libre and google for the names of any Argentine artists who's works you like. If you include the words" mercado libre" as well as the artist's name in the google search you may be able to find completed or finalized listings for paintings of the artist and see if their paintigs have sold and the asking/selling prices.
Celestino used to have a gallery on Arroyo and consigned lots of paintings in the auctions at the Banco Ciudad (which is down the block and across the street at Esmeralda 666). The final auction prices were always substantially lower than the retail prices in the gallery.
If the Banco Ciudad is still holding auctions on weekdays in the afternoon, they are worth going to. It used to be possible to see the paintings up until the day before the auctions in the lobby of the bank. It was necssary to tell the security guard that you wanted to see the paintings for the subasta. Be sure to have you ID with you.
If you click on the link in my"signature" (below) and then click on "view my complete profile" you will find links to blogs of several Argentine artists that I like as well as "The Lost Art of San Telmo" which includes paintings I bought that were in a crawl space above an office in San Telmo in 2007. I had to use a flashlight to see the paintings.