You can probably buy regular sparklers in a cotilón (party supply stores) but I'm not positive-I know they have the sparkler candles for sure. Around fireworks time (Christmas, New Year's) there are vendors in the streets. Good luck.
Great recommendation..Ive shopped inm the one opposite Ferro Carril Oeste sports club and it has a great selection....fyi for fireworks lovers, at Christmas they set up a fireworks stall in the carpark of Jumbo Palermo shopping as the people here are crazy for fireworks especially on New years eve.. I love it!