How many different right-handed Power Swords are there on the sprues of the Space Marines?
Alright, I have done some more research, asked around and I have come to the following conclusion regarding the Power Weapons on the sprues of the regular Space Marines. Some are entire arms, others are just hands. Likewise some weapons have one bladed edge, the others two.

Tactical Marines Squad


1 left-handed double-bladed Power Sword, hand.


Assault Marines Squad


1 left-handed double-bladed Power Sword, arm.
1 left-handed single-bladed Power Axe, arm.


(Note: on the older sprues these are both right-handed)

Devastator Marines Squad


1 left-handed double-bladed Power Sword, hand.
1 left-handed single-bladed Power Axe, hand.


(Note: this is on the sprues of the new boxed set)

Vanguard Veterans


1 right-handed single-bladed Power Sword, hand.
1 right-handed single-bladed Power Axe, hand.


Command Squad


1 left-handed double-bladed Power Sword, arm. Note that this one is intended for the Company Champion, not for the Sergeant as is usual.


Space Marine Commander


1 left-handed double-bladed Power Sword, arm.