How do you get contact info for parents in kids class to arrange play dates?

My kiddo is in kindergarten and wants to invite one or more kids in his class over for a play date, and I am at a loss for how to get their contact info.

In his last school (pre-k), there was a school wide Halloween party, and I met some parents there, and got contact info. Then I later sent birthday invites to the whole class (put them in folders at school) and met other parents that way.

At current school there is an app for teacher to message parents, but parents can’t message each other. There isn’t a class phone list or anything like we had when I was a kid.

How do parents get each others info in this day and age?