If nobody has responded by now,that doesn't mean people don't use it, but probably means that nobody has ID'd a single best spectacular source. I've ordered coir bricks from two different hydro shops. No problems. And someone from somewhere once said they take 1/4" or 1/2" coconut husk chips (CHCs), and grind them up in a blender to create coir for seedlings on the spot. As one has observed, shredding or grinding CHC into coir is probably best done when damp or soaking wet - not dry.

Dear Rersoap,
I sometimes use a seed starter mix to start seedlings for hydroponics. Some gardening programs on TV advocate using coconut coir mixed with fine sand for starting seedlings.
I buy most of my seedlings from Plant Nurseries, and sometimes plant the seeds directly into my coarse sand medium. What is important, is to wash all of the seed raising mix, whether commercially grown or home-made coir and sand from the seedling's roots before planting out into the hydroponic medium. This helps to keep the medium clean.
Please have a look at my web site from Australia. It will tell you just about everything you need to know about hydroponics, except lighting systems which we do not need, as we have ample sunlight all year round.
Jimr007
Australia.

Here is a link that might be useful: Simple Sand Hydroponics

Go to www.growstuffplus.com they are in Natrona Hts,Pa