Yeah, we all know how heavy and cumbersome that moss can be. Just the thought of having to stoop down to pick some up makes me break out in a sweat!
<Just joking>
Seriously, though, I did a google search for bonsai moss and was rewarded with several online stores that sell the stuff fairly cheaply. I suggest you do the same and decide which one you like best, if you can't find a local store that sells it.
Regards,
John