Meh. I think your problem is that you don't believe enough in RNGesus. Praise him \o/
More seriously (even if i doubt i'll teach you anything, it will maybe help new players) to increase your chance of getting weapons, farm standard raid instead of expert (more drop per bp).
Open it if an alt account, ensure mvp by doing ~half of the boss alone if you have low damage comparing to other players.
Farm it with stamina between events.