So at the momment, I have found that Arturo Rodriguez is like the only main Weaponry trader but I have killed him and only him, the other traders in Diamond city are still available but Arturo Rodriguez is still dead and so I can't trade with him any weaponry, so does anyone know any where else I can find good weapons to buy or how to get Arturo back alive? I can reload a save but that will send me back 2 days which is longg.

Haha why did you decide to just randomly kill Arturo and nobody else? I don't recall if he sells any specific weapons or armor you may have missed out on, but he definitely isn't the main weapon dealer.

You've got all the caravans including Cricket who's solely a weapon dealer. She has impressive inventory and can usually be found outside of Vault 81 or Diamond City. If you progress the BoS you can get access to a new location which has its own weapon dealer, and I'm pretty sure there's a robot weapon dealer in Goodneighbor. Vault 81 has a general store that has a selection of weapons including the Overseer's Guardian. Plenty of options out there and I'm sure I missed a ton.