"dandelion greens or endive? I already give them romaine lettuce. Would a variety of dandelion greens and cucumbers be better?"
Whatever you can find which has calcium. I give my turtle bok choy which isn't on the chart (but has plenty of calcium)...but is can be found in Asian grocery stores only...another trick is if the turtle won't eat the veggies raw try boiling and blanching them that's how my turtle started eating healthy foods good luck:)