Not sure where you are, but I like to get most of my supplies from Kelley's Korner Orchid supply in Kittery, Maine. The owners, Ulla and Jan, are lovely people (they are in my society also). www.kkorchid.com
For Prime Agra (cause I grow in S/H) I used to buy from Ray www.firstrays.com but he's changed his formula so I am trying to recycle what I have.
The way I pick my source is:
- what I'm looking for (different sources for long fibre sphag and CHC etc, pre-mixed or not? big quantities or not?)
- quality of the product
- and distance aka shipping cost....