I am sorry I cannot help with your particular question. But, if one does not exist, you can always use a simple hook and eye or maybe a chain lock.

I think if you foresee siblings using the jack and jill bath to go into their sibling's room, that would be a reason not to have that style of bath. I think having locks that make it possible to lock someone inside the bathroom would be a safety issue. Also, pocket doors are loud-- they aren't a great choice for doors that are likely to be used in the middle of the night.

FWIW, my kids aren't all that interested in going into each other's rooms without permission (and especially not while someone is dressing), but if they had a jack and jill style bath, I'd expect them to use it in a way that respect's their sibling's privacy.

Our hall bath had a pocket door, which was great, bu thte latch was hard to use. For our family, it was not a problem, and most guests used a powder room. Overnight guests, we just convinced them that in our house no one ever opens a closed bathroom door, it's like a visual lock. Really, the kids were good about that and not walking in on each other.

Another house, built in '52, has a very easy-to-use latch. It kind of flipped, instead of turn. I wish I'd searched harder for a proper latch when doing my hall bath, instead of going with what was at HD.