Last year, I purchased a few bags of the Espoma Rock Phosphate at the Co-Op store in Murfreesboro. It has a somewhat "granular" consistency.
They had the large bags (about 35lbs, I can't remember exactly) for a little over $20.00 per bag.
I haven't seen that there lately, but they seem to stock on a seasonal basis... so, maybe they will have more in February or March.

I, too, would be interested in learning about other sources of Rock Phosphate (and Greensand) in the area.
I would like to get some Pickup Truck loads of the stuff.