Bontrager's Surplus in White Pigeon, MI has the screws and they sell them by the pound.
My buddy here in town specializes in rivets for race cars and has the color matched rivets in stock. They are plenty strong for the application, but when I discussed this with him for my toter project (I had the same idea) he steered me away from them due to the hole in the center of the rivet you end up with. He suggested a different sealed rivet style that has no hole in the center. Still installs like a pop rivet, here is a link:
Cizmar Racing Supply / Closed End Rivets He has to order those for you as they don't usually use those on race cars. Also pick up an air rivet gun from him, they are cheap but priceless in saving hand cramps when you have a bunch to install. Greg at Cizmar Racing 330-539-3278
One bonus of using the rivets if you are less than coordinated like me is that there is no chance of the screwdriver bit skipping across your aluminum when it slips off the screw.