The information that the L5 version of this gun drops from hulks is based on a 2nd hand comment from New Players chat. During another recent conversation it was suggested they might come from pop-rock mobs instead. The L3 comes from a combat job mob (Fringe Horror) which may also be a pop-rock mob from low-level pop-rocks (which are not well catalogued). So in addition to hulks you might try low-mid level combat jobs and/or pop-rocks in the L4-6 range.
The Buckshot range of Projectile Launchers is made in a number of levels:
