Shadowing and volunteering are essentially the same thing, at least for when I got hours. I usually went through the volunteer department who set me up to shadow a therapist. If you have the time, maybe see about getting a part-time tech job. You will be able to be on site for a longer time and be able to do stuff. When I shadowed, I would just watch all day, but as a tech (acute), I was able to join in and actually help with treatments. I learned so much.