For this you do not have to mod 10 different weapons , or craft 10 different mods. You can simply mod the same weapon with the same mod 10 times. To craft a mod you need to build the accessories area in your camp. I think the first thing I was able make was a scope for either the bow or cross bow, you will need broken glasses for this and they can be found on the "A Whiff of Gunpowder" mission given by Kovac in the bunker.
Search around the level until you find them then go make the mod, then in your inventor click the menu button beside the weapon and drag the mod to the correct slot , confirm and then go back in and remove it form the slot. Repeat 9 more times.