Just a good rule of thumb is that MJ plants can handle 1/4 strengh of what most ferts reccomend.. As for the superthrive I'm pretty sure they don't have it in the states.. at least not by that name. I have family in canada ship me the stuff... It's usually at most online grow shops Insidesun.com is a good source it'd probably cost you about $10 with shipping and all but seing as you can't find it anywhere it's really you're only option. I myself do not notice much difference in the growth rate of a seedling treated with a superthrive solution, so you could just keep giving her normal water until you re-pot with ferts.