Why don't you try googling it first?
Or calling your local agricultural extension and asking the nice folks there? ( Yer growing organic tomatos, of course)
Or the good folks @ Agway.

It's going to be tough for any of us to know what's on the shelves at your local hardware store- but easy for you to ask the grandmother down the street what she uses, and where she gets it.

I'd tell you to just use Foxfarm, but then you'd be asking where to get it. ( @ the hydro store. Nice, but pricey)

Try googling " Rodale Institute". You will find many wonderful things there.