Check out Fungi Perfecti.
www.fungi.com ~$8 shipped for enough to do 150-250 plants.
I use the MycoGrow Soluble.
I don't add it to the soil, kinda wasteful, just inoculate with a soil drench at the first transplant. ONE application is all that's needed. Or, do a soil drench before you transplant the seedling.
Another good source is
www.bioag.com Humic and Fulvic acids also. High quality, good prices.
Wet