If you don't want to airbrush, I would suggest Testors Model Master buffable Metalizers. You can get them in a regular spray can and work very well. They are lacquer based so make sure what ever will be underneath it is compatable.
Tamiya 85030 TS-30 silver leaf lacquer in a spray can is a good match for aluminum. I've been using it in on styrene in conjunction with aluminum tubing and it's a dead ringer for the metal.