I'm pretty sure all the green/fresh greens are types of cabbage. they went down very well when I had pigs. You're not supposed to feed them too much cabbage though. and if one of your pigs seems to suffer from gas a lot you should probably go easy on it. What about sprouts/tops, broccoli/ leaves and cauliflower leaves? I should think they are all available in a green grocers.
You could buy one of the salad bags from Tesco or another super market, but make sure it doesn't have ice berg in as a few bags do. They have some rocket and spinach in too and the pigs liked the variety I found. (Something like
this although own-brand will be cheaper).
I looked online at a few vegetable box deliveries, and a couple seemed to contain chard. They look a bit pricey but they also contain lettuces and cabbage and every other type of veg you can imagine so they could be an option.
If you have a garden you can always pick grass, dandelions, clover etc for some greenery.
I've never seen the veggies you mention either so perhaps it's just that what's popular in the USA isn't grown much over here. Maybe you could grow some of the things yourself next year?
Well I doubt this helps much but oh well
