You can get alfalfa sprouting seeds and mung beans at the health food store. The seeds will most likely come pre-packaged and the mung beans can usually be gotten from the bulk bins. I get them organic, they're super cheap too! They have a great, crunchy/sweet taste and are full of good protein- I find that they really complete a salad meal, or round out a juice, helping you feel full:)
Heres the nurtitional info on the mung bean sprouts:
I guess you may want to stay away from your dandelion greens then, lol. If ever you come across a neighbour that has plenty, you can ask how they treat their yard and then ask politely if you may take their weeds! Yea, they may look at you funny, but heck, you'd be helping them out, since most people go to great lengths to get rid of weeds!
Frankly now that I've been gathering greens, I am always looking at everyone's yards on the way home, thinking, hmm, I could eat that...hmmm, do I take a bunch? LOL, it's become a fun game:)
You can also try growing stuff indoors I am sure, like herbs and such. I haven't yet, but it would be so nice to have some herbs in pots, like parsley and oregano, to really spice up whatever I'm eating/drinking, especially in the winter!