My friend, you are in luck.
I have java moss up the ass that can probably cover a 10g.
Also have riccia that I've grown floating, don't know if you'd still want.
Meet me in Brooklyn (brooklyn zoo and aquarium) and its all yours for free.
Edit: Didn't see the clean part. There might be probably flame moss or some other common moss mixed with the java moss. Also not MTS free.
Lmk if still interested. Also leaving the city very soon so kinda urgent if you want em.
