I found some at Target that although did have the shelf in them it was big and generous and not really supportive so maybe you could Dr it up and cut that elastic bit out??? They only had slits in the inside shelf bit for your boobs not an actual cup so you had to wear a bra with them anyway.
I think I found them in the maternity section and they went up to size 26 so lots of wiggle room and very comfy. It was 2 summers ago that I got them though so hopefully they still stock them.