While it's not all that difficult to find impromptu musical performances in Hawaii, they're usually traditional Hawaiian music with slack-key guitar and ukulele. I recommend seeking those out even if there's not usually much call for percussion, although there may occasionally be some congas and shakers as there were at a jam I attended last week on the Big Island.
I haven't seen that many rock-type jams in the Islands, and I've sought them out.
Some of the hotels on the west side of Maui might have Hawaiian entertainment and you might also find some more drumset-oriented music in Lahaina. Gene Simmons and Paul Stanley of KISS recently opened one of their Rock 'n' Brews restaurants in Paia and they might have bands. http://www.rockandbrews.com/paia/
Here's a place to start: http://www.gohawaii.com/maui
You didn't ask, but I'm going to give you some dining recommendations: You'll have to drive by here to get to Lahaina and Ka'anapali, but you mustn't miss Leoda's Kitchen and Pie Shop. http://www.leodas.com/. If you like fresh fish, there aren't too many places where you can go wrong, but you'll save a ton of money if you visit the Paia Fish Market (http://www.paiafishmarket.com/) instead of Mama's Seafood House. Mama's isn't bad, it's just very expensive.
Have a good trip. PM me if you want more recommendations, I edit the AAA magazine for Hawaii.
Al