I have been working on getting my horse on the bit for a couple of months now and let me tell you Kayty's post about consistent and patient work is so true. LOTS of work. I have the kind of hunter school master who knows all his stuff but will only give it to you if you ask properly/ride him correctly. Someone with an educated seat and hands can put him on the bit and in the perfect hunter frame in a heart beat, but me, I cheer if I have him round and stepping under himself for more than one full go round the arena. It's lovely to see my coach get on him and show me what he can do, but also can be a bit frustrating at how much time it takes to get there. It is more about you and your seat and riding than a magical trick or just the right bit.
Funny enough, when we hack out and trail ride I can get him framed up and on the bit in no time, almost without even thinking about it. I think I am more relaxed and balanced when I'm not trying so hard. Are you working with a coach who can help you on this? It's the kind of thing that is hard to learn but becomes more automatic the more time you put in doing it.