I've always felt that if you really have to stress the muscles and tendons and send a shock through your nerves to really trigger the growth.
If you look at a lot of armwrestlers that only pull with their right arm, that forearm is a lot bigger than the other. The stress they put on their tendons and nerves is substantial compared to doing little wrist curls at the gym.
On a side note you don't have to arm wrestle to get big forearms lol
If you work out the forearms adding pronation and supination workouts it'll definitely improve them. Hand strength also improves them.
I would guess heavier lifts that put a lot of strain on the calves would really help, but I've always felt that if you walk a lot all day and do calve workouts you tend to break down the calve muscles. I know some guys that sit all day at work and have massive calves. Probably genetics there, but if you want a muscle to lose size, overworking it is a good way.
Just a few hypothesis' I've come up with. I have pretty small calves, and I'd like to put my theories to the test. With a cycle of course...coming this winter!