You have gotten some excellent suggestions. I would add two things for variety. Not strictly a forearm exercise, but will benefit the whole arm, inlcuding the forearm.
Reverse curls with a cambered bar and hammer curls. You will be strengthening the brachio-radialis (supinator longus), extensor carpi radialis longior. The former arises from the upper 2/3 of the external supracondylar ridge of the humerous, and from the external intermuscular septum and the fibers terminate above the middle of the forearm in a flat tendon, which is inserted which is inserted into the outer side of the base of the styloid process of the radius. The latter arises from the lower 1/3 of the external supracondylar ridge of the humerous and from the external intermuscular septum by a few fibers from the common tendon of origin of the Extesnor muscles of the forearm. The fibers terminate at the upper 1/3 of the forearm in a flat tendon, which runs along the outer border of the radius, and finally to its insertion at the base of the metacarpal bone of the index finger.
It is funny to see someone do as many "regular" curls, hand in a pronated position-palm facing forward with hand by your side. Then then they cannot do another rep, have them rotate their hand so the thumb faces forward and they can crank out reps. Thanks to the muscles above.