Guess it depends on how close you feel you have to get to the original grey. If it was me and I didn't already have the paint to mix, I'd probably go with whatever grey Eastwood or some other mail order house sells. I don't buy much spray paint from hardware or auto parts stores anymore because it's generally pretty crummy stuff, what with the current laws here in Santa Clara County.
But as it happened I already had some Imron white and black paint on hand. I mixed it to the shade of grey I wanted and shot my bows with an airbrush. Not much effort involved.
Another option might be POR15. I think it comes in white and black.
Roland