A different slant of gaining forearm size and strength:
Reverse BB curls. Have the thumbs over the bar (thumbs and fingers both on top of the bar), that's called a false grip. This and the regular reverse BB curl is a much over looked bicep & forearm builder it's self. Might try alternating both grips from workout to workout and use both style in the same workout.
Quite a few BB'ing will use the false grip when doing DL's, cable pulls, regular chins, curls, lateral/front raises,etc, etc, etc..
Hang from a overhead chinning bar with both hands, with just the finger tips gripping and keeping the thumbs out of the way. Now try curling the grip inwards as much as you can, than release slowly. That would be one rep. Can also do this on an overhead beam, 6 by 6, or whateven.
A couple of rock climbers taught me this gripping exercises a few years ago. They were at the point of doing these one arm at a time...or while holding a DB (sometimes with a heavy sand bag or back pack..even more of a challenge for the grip) in the non chinning hand. They also held that gripping position for a minute or two as part of training.
Assuming the two hand pushup position, with the hand/fingers straight ahead & shoulder width, try raising up to the finger tips, all the way up, for reps.
Good Luck.