If he's in Kindermusik they should be expecting all the kids to be moving around, distracted, wiggly! We didn't do Kindermusik but did lots of sessions of the somewhat similar Music Together program for kids this age and your son would never have been expected to stay still -- if his current Kindermusik teacher does expect this, find him a different teacher or move to another music program! Is this parent-and-child so you're there with him? Don't hold him on your lap etc. -- it should be fine to be up walking in the background with him. A good teacher should get things up and moving so no kid is expected to be still for more than a few moments.
Same with library story time. If he's in the appropriate age group for that story time they should be fine with his moving around -- again, not up at the front in the leader's face and in front of (and distracting) other quieter kids, but in the back on on the side. Just fine. Be sure that you are taking him to story times that are age-appropriate; sometimes libraries will note that a particular story time is for ages 3 and up, or infant through age 2 or whatever; be sure you're checking, and if you don't know, ask someone -- just call.
Please get some books on age expectations for young children. It's not realistic to expect a child under three to sit down, face front, stay silent for more than a few moments. Any activity he attends should be right for his age group and should encourage movement instead of being a sit-down affair.
Consider much more active things like My Little Gym or Gymboree classes or similar (and much cheaper) classes at your local parks and recreation department. Ours had lots of "mommy and me" "Wiggles and Giggles" classes where parents brought kids your son's age and a very lively teacher had the kids climbing over mats, playing loud games, etc. This is what he needs to be doing, not sitting still the whole time.