You will find a rich array of musical offerings on the website of the Isabella Stewart Gardner Museum, including a fair bit of new music. Go here and sort by composer; you’ll find music by Sean Shepherd, Caroline Shaw, Fred Lerdahl, Helen Grime, Leon Kirchner, and Andrew Norman, among others. (Call me paranoid, but I note that the default sort when you arrive at that page is by performer, not composer.) There are some videos of works by contemporary composers (alongside modern classics) here.