if you want to do it by the book, you will need to hand the ammo over to an FFL where you live, and have them send it to your son's FFL, who would then do a background check before handing it over to him. to pass the background check he must have bought a gun in california in the last 5 years and not be on the prohibited persons list (felons etc). most FFLs here charge $5-10$ per case and are not keen to share their info with strangers. i'd say best chance to get someone to agree would be to send it through a major gun store that they already deal with (if you can convince the store on your end to help you). all in all, it's going to take a lot of searching and hassle to find anyone who will do it.


as far as driving it across the border, you can legally do that yourself if it's a small amount and you are coming to california on a hunting trip, but he can't cross the state line to pick it up and bring it back. but if you did decided to take a road trip, the biggest contraband they are searching for at checkpoints on the highway is citrus fruit. hint hint.