Not a "where" but... when you have your own kid(s), you tend to make friends with your kid's friend's parents. Many continue to have children over the years and you'll get to see lots up close. Just be excited for them and don't be weird about it. I've gotten to feel quite a few of my friends bellies and even got a couple of long sessions feeling movement. Anyone finds that pretty amazing, not just us!

Take a walk around malls. Malls with maternity stores and children's clothes usually draw in more pregnant women.