Where can I find a 1/2" bit screwdriver?
This sounds like a job for a socket wrench. 

Because a socket wrench has a long handle, it acts like a lever and you can get a huge amount of torque from it, MUCH more than you can get from a screwdriver. 

You can get driver bits for those as well, but since you said 'bolt' and it's 1/2", that it will have a hex head on it that you can use a socket bit on.

Using some penetrating oil or WD-40 on the threads may also help to loosen it if it's rusted or corroded.