Thank goodness for the chamber music societies that fill up the calendar with intriguing music for not much money. In November, the Mill Valley Chamber Music Society presents Concertante, a well-established string ensemble that last year finished an impressive two-year commissioning project that included such composers as Lowell Lieberman, Gabriela Lena Frank, Shulamit Ran, Kevin Puts, Tigran Mansourian, and Richard Danielpour. It wouldn't be surprising if one or more of these pieces made it onto their program in Mill Valley. Fans of new and non-warhorse repertory should make time.