This thread might give you some ideas :
http://www.largeformatphotography.in...t=29267&page=5
Basically, if you have the original bellows material, measure it, and this gives you the dimensions of each side. Then measure the size of each pleat stiffener, and the distance apart. Then draw it out in a graphics program.
That should give you your pattern, which you can use for what ever method of construction you are going to use.