There's
Spanglish Exchange on Thursdays and Saturdays at 7pm at Rabia Bar in Palermo. This is a structured event where groups rotate, with half the time spent speaking in English and the other half spent speaking in Spanish.
Mundolingo has a bunch of events and is helpful for meeting people. The Friday event has a lot of people, but is more of a singles mixer than a serious language exchange.
On Saturdays at Tavern 1747, a language exchange from 8 pm to 11 pm. Super relaxed, I get the sense there's a bunch of regulars who go. It could be a good option as you get more confident.
Thursdays at Queen's Ale House at 7 pm in Palermo/Villa Crespo. They also have karaoke, which starts around 10pm.
I'm sure there are tons of other events I'm not aware of. MeetUp can also be a good site to find them.