If you can't find it, then I would recommend using
long romaine leaves, that would work too!
Not exact matches
Butter lettuce and
romaine leaves are ideal, but cabbage and collard greens also work so
long as you balance the bitter flavor with a sweet or spicy protein filling.
Instead of using bread, I served it on top of
romaine lettuce
leaves for a lunch last weekend, and my family loved it (they also said this was the best chicken salad they have had in so
long).