If you have a 24 inch barrel, use the standard Garand op rod spring; min/max 19.75 inches/20.25 inches. If you have one of the Tipo 2 7.62 Garands with the .5 inch shorter barrel, shorten the op rod spring to 19.25 inches. The standard ejector springs work fine. If the brass flies too far away, remove a coil from the ejector spring.
Both Numrich/GPC and Brownells sell new springs.