Fixer Uper

[SilverAg08]

I am new to the forums, but yesterday my father and I drove to a rural Texas town and picked up a 2001 GZ250. We got the bike trough a family friend for free but the bike had been sitting in her garage for about 5 years. Driving out there yesterday we didn't really have a clue what awaited us, we really weren't even sure of the make or model. What we wound up with was a bike with 256.3 miles on it with a dead battery, varnished gas and rusted tank, slight pitting on all the chrome and flat tires.

The Good: the tires are inflated now and holding air, and for all intents and purposes are brand new.
with a little elbow grease the pitting can be removed and she can be back to showroom sheen in no time

The Bad (stuff I need help with): The tank was bad... really bad. We cleaned it out as best we could but are thinking that a new tank might be the best solution. Is there any place ya'll know of or would recommend to get a tank from? What's the going price on the tank?
Also the battery is essentially a black brick. we tried charging it but its not taking. Is this battery readily available at your average AutoZone?
On the pitting, is there any method you are aware of that is especially effective at removing pitting? Right now I'm trying rubbing compound and turtle wax chrome polish and rust remover... its doing a decent job but if there is a better way I'm all for trying it.
tia