I couldn't find where a second thread had been started and the original one has reached maximum posts.
Turface MVP : Whittlesy Landscap Supplies $13 bag
Gran-I-grit : Buckmore Feed and Pet Supply
Fir Bark : Ordered from Amazon and ran it through our mulch machine to make it smaller.
An update for any forum members in the UK:
Moler clay: sold as Moler/Terramol, 25 litre bags, Kaizen bonsai. (they also sell pumice).
Pine bark: BHGS Ltd, Evesham and ask for Melcourt Propagating Bark, 70 litre bags.
Also, if you don't want to make your own gritty mix, and you just want to buy something ready-made, take a look at Kaizen bonsai Premium Bonsai Compost No. 3 - it looks very, very close to Al's gritty mix!!
AGWAY - Store Locator:
I found all components in my Mechanicsburg, PA store.
Grani-grit, TurfAce and Agway pine bark mulch.
They have locations in PA-NJ-NY-CT-MA-VT-NH and ME