Fat Gripz on a pullup bar. Your forearms will be on fire but they'll have no choice but to get stronger. You can make something like these for pretty cheap (heck you could just wrap a towel around the bar), but they give you an idea of what you'll want to do.
Also you could get into rock climbing. It's fun as hell and your grip strength goes up quickly.
What size Fat Gripz did you buy? Thanks!
You can buy fat grips that’ll help you’re forearms grow while doing other lifts. https://www.amazon.com/Fat-Gripz-Forearms-Diameter-Soldiers/dp/B07TVVBPP2
Hey King,
This is based off past experience, but I'd recommend adding in 3 sets of Hammer (dumbbells) Curls at a slightly lighter weight. They would end up hitting your biceps at a different angle and engaging the muscles in the wrists and forearms.
Another thing I would recommend (and something I swear by) is a product called Fat Grips. These helped me out back in the day and I've recently began using them again upon my inevitable return to the shrine of gains.
Hope this helps!
-Trys