Out where I live, there is the store, the Care Connection, and it is a store that exists for breastfeeding Moms. It is a wonderful store and a fantastic resource!! You can order the larger flanges right from them ... I have the 27mm, and I know they carry larger one. I believe you can order online, but if not, you can do it through their toll free number.
Here's their site:
http://www.careconnectiononline.com/
and their number is: 1-877-639-0300
Sherry is the owner, and she is so helpful.