Just take the car to a car paint merchant and they'll match it for you, put some in an aerosol, sell you just about anything you need (etching primer, wet or dry, masking tape, gel, etc) to do the job, generally at better prices than motor factors.
I would just go to your nearest automotive paint supplier and ask to see the swatches of metallic greys and silvers and pick one. They will have loads to choose from so just pick one you like, doesn't have to be exactly the same surely.