Your just a little late. Frank Macey, the keeper of Jim Walkers legacy passed away recently and as far as I know the supply of Walker memorabilia may soon dry up. A few years ago he had done a few replica kits of the Fireball for around $125.00 but these are now collectables and are seldom seen or sold.
Replicating this kit would be an expensive proposition as the block of balsa that that fuselage was made out of would set you back a small fortune to buy , if you could get on that size in anything approching decent weight and density. Plans still might be available. You might be able to get some help from the walker site.
Dennis

http://www.americanjuniorclassics.com/