Hi, I'm from Buenos Aires. You won't find any decent knife shops here, most discerning Argentine knife enthusiasts order their stuff from the US or bring it back from trips abroad. There's only one place, a gun store called "Miranda" on Bartolomé Mitre and Paraná (Bartolomé Mitre 1495), that stocks brands like Spyderco, Benchmade, Zero Tolerance, Protech, Emerson, Ka-Bar, ESEE, Ka-Bar, etc. But prices are way higher than what you'll find in the US. In case you decide to go there, ask for Sebastián and tell him Francisco sent you. He's a good mate of mine.
As you probably know, tomorrow is a holiday (Independence Day), it's a good chance to take a day trip to San Antonio de Areco. It's a nice little town close to BA in which Argentine rural traditions and the "gaucho" life style is still kept alive (112km, less than an hour through a big highway, there are buses from Retiro that take an hour and a half). There are several excellent silversmiths who do beautiful work and whose workshops are open to the public (you'll see amazing knives!). It was the home of one of our most celebrated folk tale authors (Ricardo Güiraldes). On holidays and weekends there are usually horsemanship shows, folk dances and other activities.
http://www.sanantoniodeareco.com/turismo/index.php
I'm a country boy at heart, and raised horses close to San Antonio de Areco, that's why my first advice on what to do in Buenos Aires is to get out of the city and away from
porteños.

But there's a ton of cool stuff to do in BA as well.
If you need anything, just send me a message and I'll give you my e-mail address.