Did some research,
Great question. There are actually several scholarships available, which you can read about here. You just need to scroll down to the section for 'Scholarships for ADHD Students' at the bottom of the page. They include:
The Michael Yasick ADHD Scholarship by Shire recognizes and supports individuals diagnosed with ADHD in the US who are pursuing higher education. Applications are now closed for 2014 but you can get updates for 2015 here.
The Anne Ford Scholarship is supported by the National Center for Learning Disabilities. The $10,000 scholarship is open to graduating high school seniors with a documented learning disability.
The Novotni Scholarship Fund is administered by the Attention Deficit Disorder Association with annual awards ranging from $1000 to $5000.
I hope that helps!