Ok, I triple check the chart and maybe @bpatters
can double check my suggestions:
You can feed daily: 25 gm of cilantro, 1 baby carrot, 1-2 cherry tomatoes.
You can feed 2-4 times per week: 25 gm of parsley, a slice of a red tomato, slice of cucumber.
Since you only have romaine as a lettuce: I would start feeding eat and check the urine for calcium deposits. There are some pigs that have no effect whatsoever from romaine and you may luck out with yours. But if you notice calcium residue in the urine (usually a white, chalky residue) you will hace to decrease the romaine.
Swiss chard is very high in calcium so I would have care feeding it more than 2-3 times per week.
I think I covered all the vegetables you mentioned. What about peppers? Can you find some green peppers? They are very high in Vitamin C and can be fed daily.
Believe me, lettuce is relatively easy to grow from seeds and peppers as well. As soon as i find a new house to move into I'm starting my own vegetable garden for the piggies and for myself. I will be using heirloom seeds to avoid GMO's.