I do give mine spring greens but about a leaf each a day at different times, brocolli is also gassy but i give them small amounts of that. I give them celery and celery leaves (chopped up), as a treat they get baby sweetcorn and small amounts of carrot and apple (the last two are quite high in sugar so only on occasion) Also mine like watercress and you can give them rocket although mine are not that keen. I sometimes get carrots with the tops on they love the tops off carrots. I also give them cauliflower leaves and also curly kale.
I also collect loads of forage for them like dandilions, grass, plantain, clover brambles, hawthorne and beach leaves.