I can find coconuts with the husk in brooklyn ny at markets and street stands...
I the summer I could get a bunch of discarded coconuts husk after people had drank the water in it.
if you want to drink the water a small coconut is $2 up to 3 or 4 bucks for the larger ones.

I noticed some are yellow and some are green. what is the difference?

Anyway coconut is the best media for me by far. It can dry fast.
stefano