Andy, try a pet supply store. Someone over at Dave's told me "You can get coir at any petstore. I buy it at Petsmart. It's used for bedding of small animals. It's sold by brick and is not expensive."
There are also bricks for sale over at Dave's Garden Marketplace:
Searching Dave's Garden
I know this guy is reputable:
Coconut Coir - Instagarden His name is Boca Bob, and he is selling on the Dave's Garden Marketplace also.
I think it's also sold on Ebay.
You could try Western Farm Service in Oxnard. I know they have the fiber coir for sure. It has a lot of peaty texture to it as well.