Pack a suitcase full of hair supplies?
Other than that, when I was in Peru, there were boticas on every corner with hair products. Not a huge selection, but if you're going to be there for four months, you probably speak Spanish well enough to figure out the equivalent -cones in Spanish. And the larger grocery stores carried quite a few hair products. I'm part of the cg on a budget crowd, so I'd be all for experimenting.
OH! And, BA is a large city, so they probably have high end salons, just like Lima did, where you can get higher quality stuff if that's what you're about.
Hope this helps