Chuck Moline at Warpath Vintage on facebook, he is the chuckindenver mentioned above and is one of the go to guys for 1903, 1903A3, 1903A4, as well as many others.
If your stock is one of the new CMP stocks, you will want to check the fit of the stock first and adjust as necessary. Check the CMP forums for a lot of info. If they are using the same stain they used to use, you will need to strip it off or new finishes will not penetrate into the wood.
I...