Here's something good. You can go to any supermarket in south-central (e.g., the Ralph's at the corner of Crenshaw and Rodeo), and they'll have a huge variety of fresh greens, "Cut and Clean" brand, packaged ready-to-use in cellophane bags. They have mustard, turnip, collard, and others that aren't so widely available elsewhere. (They also have several varieties of canned prepared greens.)
These greens have a good "bite" to them, and they work well in cooking. For example, I made a pork and vegetable stew with chipotles and turnip greens. After degreasing the pork overnight in the fridge, I put it on the stove and dumped in a one-pound bag of turnip greens. Not precisely traditional Southern cooking, but excellent.