Not a specific event, but you can use the ObObjectEquipped event and place a condition to check for a left or right hand weapon inside.
Event OnObjectEquipped(Form akBaseObject, ObjectReference akReference)if akBaseObject as Weapon player = Game.GetPlayer() if player.GetEquippedItemType(1) > 0;1 is the right hand, 0 is the left hand .... endifendifendEvent
Of course, this means the condition is met every time you equip a weapon and have something in your right hand. This does not check if the weapon you equipped actually went into the right hand, so the condition will also be met when you have a weapon in your right hand and equip something into your left. I'm not sure what you are actually trying to do, but maybe this can get you on the right track.