Meg. Get a basic hollow ground screwdriver set. And a two sets of punches. One steel and one brass. He will also need a hammer. Mine has interchangable heads. Steel, Brass and plastic. RThat would get him started with the most basic gunsmithing tools. And he could do alot with them. Swapping parts etc. If he has spare parts for his guns this would be all he would need for repairs.
Then from there get him some kind of Dremel like tool with the extension shaft. To make parts he will need a drill press, a mill, lathe, table grinder etc. These can all be table top models for most parts. This would be more advanced though.