I don't know anything about the coconut bark, but can help you with your original quest -- to find coconut fiber. Lots of garden centers have it, but they sell it in rolls, or pieces. You've probably seen it and just didn't realize that's what it was (that's what happened to me, anyway...). It's the brown, wiry, peat-moss-looking stuff used to line hanging baskets. Check this out:
http://www.yardzooks.com/mm5/Replacemen ... 7QodfiOfJg(by the way -- I'm not recommending Yardzooks -- I just wanted to give you a picture...)
Once you have your piece, or roll, you can cut or tear it to put it in your homemade potting mix. (It's MUCH easier to cut it, than tear it...)
Happy gardening!
_________________
God speed!
Cara
**
Take time to stop and smell the flowers!
(or... as my ladybug refrigerator magnet says
"take time to stop and
eat the flowers!"
)