You should be able to find live music during your stay since San Pedro day festivities should be going on, see under holidays AC hompage. Usually bands play in Town Park for Festivals, also always local music too.
There are someover 50 rock-n-roll types that now live in San Pedro. I bet you would enjoy a stop at Estel's Dine by the Sea. Charlie has an awesome recording collection and loves to share his music knowledge. He played in a band when he first moved there.

Belize it!