u should be able to get worm castings at a hydro store, either that or a plant nursery, alota landscaping yards that sell sand and crushed gravel always sell bulk soil and castings, also remeber when using organic soils and amendments u need to water with de-chlorinated water, either buy distelled water, get ur own water filter, or a last resort let ur water sit out ina open container for 24hrs to let the chlorine dissapate outa the water, ul be able to smell the difference when chlorine is in the water, thats the biggest piece of advice i can give u right now is make sure ur water source is good cause chlorine is a bacteriacide and will kill off all the microlife in ur soil mix, without that microlife breakin down the nutes in ur soil ur plants wont be able to eat properly, if u have been watering with chlorinated water no worrys jus add ur worm castings and water em in with filtered water, good worm castings have alota microlife in them and that'll get things crackin