Check the frozen food section at your grocer's. I know around here it's easy to find frozen chopped collards, but I'm in the South.

Or, see if you can make friend and obtain vegetables that may be past their prime (i.e.not pretty any more) for human consumption: the produce mgr. may be able to give you a call to alert you when semi-viable produce is about to hit the dumpster. Do the same with any restaurant that might have a salad bar...

Get creative.