Grocery store type greens should make up a very small percent of a sulcatas diet. Grasses and weeds should be the main part of the diet. You can buy seeds and grow them yourself and just harvest to feed. I grow mine indoors in containers and cut what I need (I don't have a sulcata, but you could grow the foods the same).

http://www.sulcata-station.org/diet.html

You can buy seed mixes here: www.turtlestuff.com