As I was reading your post, I was thinking: Route 66. I'm the Asst. RD for the Sprint on Saturday and I'm doing the Oly on Sunday.
Let's see:
1. There's the Topeka Tinman on June 14th. Here's the site. It's just slightly longer than an oly. Swim 1100 yards, Bike 19.7miles, Run 7 miles http://www.topekatinman.com/
2. This is in July tho, so you may not be able to do it. Midwest Mayhem on July 20th in Lawrence, KS. http://www.midwestmayhemtriathlon.com/
3. There's a tri in Orange Beach on May 3rd. Just a little shorter than an oly. Swim 1000 yards, Bike 19.5 miles, Run 4.5 miles http://www.team-magic.com/

Other than those, there's not much around for June in this part of the country. It's just too hot. You could always do the Kansas 70.3 in late June...