I see you are working hard in here!
You can pick up a lot of accessory forearm work by the following: After your heavier working sets of anything...DB flat bench, lunges, etc hold the DB's, or BB on deads or shrugs, till your forearms are on fire and you wanna cry for
Time under tension will greatly improve your endurance. You can also go grab a set of DB that is say 20# more than what you use for DB shrugs and just hold them for 30 seconds or whatever it takes to make you think you can't get them back to the rack. That will get your body used to holding the higher weight.