The moss you find growing in your local area is most likelly the best moss for your bonsai. Imported moss has no guaranty to grow were you live. I have a paved patio that is a perfect habitat for a low growing moss. Same moss grows well and thrives on some of my bonsai. Collect locally is the key.
Unfortunately, it’s nearly impossible to find moss in California during the summer. It’s totally dry here right now. Unless our upcoming winter will have substantial amount of rain I would find some. The moss here is very shallow.
But how do you collect moss? Do you scrape it off and keep some of its dirt and apply it to a pot?