You really don’t want to be late to the 9:30 Club show Saturday night or you may miss a group that promises to be one of Charm City’s brightest exports. Say Chance is opening for the rocker’s Augustana and the Baltimore-based female trio is already gaining national press for their cool sound. The three members of the band — Maddie Freeman, 17, Taylor Broom, 16, and Kelly Rosenthal, 19 — met by happenstance on the Web and soon found themselves musical soulmates. So confident are they in their music that Rosenthal recently packed up her life in California and moved to Baltimore to give the band a true shot.