5g is usually agreed to be a good amount. Beyond that, Rez-V and ZMA are pretty good supplements that might help.
Fundamentally to gain size, you must eat more. Your body has a set point it is trying to maintain. What happens when you eat 3200 a day? 3400?
Size = excess calories
No matter what you do, you have to eat for size. Here's a good article from Dave Tate including a story about what it took for him to add weight past a certain point. Not saying it's healthy or anyone should do it, but you can't escape your nutrition one way or another.