Dedicated drops for unnamed weapons?

this might be a weird question but are there enemies that have a higher chance of dropping specific kinds of weapons, manufacturers, etc.?
and do you think that might be a helpful thing?
in some situations and builds, there can be BiS purple gear and that is probably even harder to farm than legendaries
the first thing you do is probably just going for some farming spots that drop a lot of stuff in general

what would you recommend for farming purple grenades and maybe also shields?