I believe that the Van Graffs at the Silver Rush have the heavy energy weapons I wanted to collect, trouble is, I pissed off the Van Graffs during Cass's quest and I don't want to kill them to earn a certain ending.

In short is there any way around this? Seems like a silly mistake to add GRA items to the merchants who in a quest you have to either kill or piss off.

Yeah I killed the Van Graffs as part of Cass' quest back at level 10....I still don't regret it, not using energy weapons anyway.

The GRA inventories of dead merchants eventualy migrate to the gun runners.

I've already obtained every GRA weapon and modification, and I killed the Van Graffs ages ago.