A/C vent problem
 

My 2000 DeVille DHS (which I have owned for 2 months) has a minor problem. Whenever I put the A/C blower on high or one notch below, the dashboard vents in the middle and sometimes the one by the drivers door shut themselves (the ones you move with the dial not the side to side). It is a real problem.I know I can try and remove the vent caps and find new ones for the car. Anyone have any other suggestions or recommendations as to where I can get replacementswivels aside from going direct to Cadillac?