Active grille blocks have existed on big rigs for a while -- ever notice the venetian-blind-like things moving out front?
A Walkman or computer fan motor will be way too weak for this purpose. I'd suggest finding a gearmotor or contacting a local robot hobby group to get some of their castoffs. In fact, they'd probably find the project intriguing and would help with the fabrication and control scheme.
Check out
All Electronics for a good selection.