Head for the Cure Foundation is a well-established fundraising non-profit for brain cancer.
They have had recent marathons in Kansas City, Missouri, and in Lawrence, Kanas.
They may have something in your area(s); or you could contact them and get something going in your area. A friend of mine who is a federal public defender in Kansas City recently ran in one of those marathons. The public defenders office organized as a group, and all participated at some level---either as runners, walkers, or volunters.