I'm from Wentworth, but I go to Sioux Falls alot.
Yes, try the BORN meetings and LLL. It's not unusual for a pregnant woman to go to LLL meetings. You could also take Bradley Birth Classes, you meet like-minded people there. I think one of the instructors has a flyer up on the East Dakotah Natural Foods bulletin board.
Or come down to the Falls Farmers Market, sometimes you see people wearing their babies there. That's generally a sign of "crunchiness". It's on Sat. mornings from 8am to 1pm across from Falls Park.