There are plenty of brainstorming apps out there currently. However, none of them help you to find better or more people to brainstorm with. How about adding in a ‘find a brainstomer’ feature within an app that helps you find the people closest to you for that impromptu brainstorm.
Add in some profile features like those found on LiveNinja and your next brainstorm could be that much better. Stop bringing the same people you always do to the session, go find some new ones.