I have a couple of friends w forearm issues who use variations of these: https://www.climbing.com/gear/forearm-therapy/

I don't remember the one I saw looking exactly like any of those, but I imagine there are a lot of versions. I think one was even homemade? Like, someone had rubber-banded together two roller sticks.

I also know a lot of climbers who use tennis balls/lacrosse balls/foam balls/foam rollers, and bodyweight to do their own massaging. There's always someone at my gym doing some sort of weird contortion to press an odd part of their body into a ball.