You can get the attacker from the damageinfo provided in the hook.
GM:ScalePlayerDamage( Player ply, number hitgroup, CTakeDamageInfo dmginfo )
That hook returns dmginfo and you can get the attacker through dmginfo:GetAttacker() or dmginfo:GetInflictor().
dmginfo:GetAttacker().Loadout would work? I have table attached to each player called ply.Loadout, would dmginfo:GetAttacker() work?
Ugh, of course it didn’t work…
Specify what you mean by “didn’t work”
You have to make sure that GetAttacker returns a player using http://wiki.garrysmod.com/page/Entity/IsPlayer