Most Garand stocks are going to be replacement stocks, even if old. There are many sources of stocks, both domestic and foreign. Overton was a common source for rebuild stocks and those might not feature a proof mark. Are there any other marks? Anything written or stamped inside the stock such as on the barrel inlet? Sometimes external marks can be very light and you might need to look in bright sunlight to find them, or if the wood is very dry you might need to apply some BLO or similar to bring them out.
There's a 'milsurps' forum here. You have to scroll down towards the bottom of the forums list to find it. I suggest posting a pic.