If you want to continue working on the model you may use the Tamiya spray can of the silver acrylic paint. Also it may be a silver or aluminium paint of other manufacturers. The main thing is it has to be the acrylic one because you used the acrylic grey paint as the primer. The colour of a different type eg enamel or lacquer may damage the grey coat. But even though the sliver should be of the acrylic kind I would check if it doesn't affect the grey one firstly.