I were looking for it myself and found something that worked.

_index = "srifle_DMR_06_hunter_F" call jn_fnc_arsenal_itemType; [_index,"srifle_DMR_06_hunter_F",-1] call jn_fnc_arsenal_addItem;
_index = "10Rnd_Mk14_762x51_Mag" call jn_fnc_arsenal_itemType; [_index,"10Rnd_Mk14_762x51_Mag",-1] call jn_fnc_arsenal_addItem;

This code can be executed locally when you pause the game to bring up the menu with ESC.

Just need to change the classnames to whatever, classnames for weapons in particular can be found here: https://community.bistudio.com/wiki/Arma_3:_CfgWeapons_Weapons