The first thing necessary in replacing a worn or broken handle is to remove all the parts and hardware associated with the top cover. If you can remove the screws holding the cover to the body your job will be easier. This can be done easily sometimes because the leather covering has come unglued on the brass hinge. Once the cover is removed the rivets can be removed. Use an automatic center punch or any center punch and mark the centers of the four rivets. Drill carefully using a drill that is smaller than the rivet (about .088"). If you did it right you can push the old rivet out. Save all of the washers and what is left of the straps. Use the old straps to make help make new ones.
I clean the old washers and then drill them out to .096" with a #41 drill. I have a Shoe Repair Shop make the new handles to my specification. The man also furnishes me with some scrap leather to make the new straps. I dye the new handles and straps black.
I tried using available materials for replacing worn Graflex handles, which included 2-56 machine screws, until I found some brass nails. I found the brass nails in, of all places, a surplus electronics store. The nails are about 1" long and have a body diameter of .096
The nails are hard drawn and must be annealed I made a jig using a piece of 1/4" aluminum plate about 11/2" X 3/4". Drill four holes with the #41 drill and set in a metal pan of water (5/16" deep) so that you will not anneal the heads plus at least 7/16" of the shank. Use a propane torch and heat the tips red hot. Cut off to the correct length about 1/2" (put one of the nails into place using the new strap and the washers for the length measurement. File the end square and leave the new rivet just a little long, about 1/32".
Make a backup tool for the rivet head that can be secured in a vice. Use a drill the size of the head of the rivet and cut a very shallow hole in the end of an old bolt or piece of steel rod.
Now assemble one of the new straps and all of the washers and the rivet
and with a small tack hammer, peen the end of the rivet Do this with another
strap and washers on the other end leaving a loose end on each end of the
cover. Now place the new handle under one of the straps and repeat the
operation again and then on to the last rivet assembly. Now the cover can
be replaced along with its hardware.