I guess it all depends on what your willing/able to do.
You could modify a stock seatpan if you have the ability and access to the tools and equipment, or you could try to find one similar from a diferent bike.
You`d have to modify the seat to fit right regardless of what its right.
Or if you want to spend you may be able to find an aftermarket item for the cb.
Whatever way you go theres time and money to be spent, how much depends on the routs you take and your abilities.
Cheers
Troppo