Dirt/Gardening

I'm trying to get a food and flower garden going at my mom's (as a mother's day gift), and was wondering if there are any ethical ways I could get dirt other than digging it up out of my own yard. I rent, so that is not an option. For the record, I first got the idea in my head that commercially available dirt could come from mountaintop removal from bfp's blog, and it deeply scares me, not least of all because I'd like to move to Appalachia to be closer to my Appalachian darling partner. Soon. I don't want to be an unwitting accomplice to damaging his home* any more than I want to unwittingly contribute to the destruction of my beloved Michigan.

Also, more experienced gardeners (I'm looking at you here, Trish and Eve_L), I have a gardening question. I bought some beans (and so did my mother, actually). I was wondering how I could maximize their nitrogen fixation benefits. Should they go in the middle of the garden? Scattered amongst the other plants? Along the edges? Any suggestions at all would be greatly appreciated.

*Seriously. Even if he didn't have other ties holding him to the area, you should hear him talk about it. It's as if no one would willingly leave the county - the only acceptable reasons for exodus are education, jobs, or being kicked out.