Hal -
I put your drawing of the special bolt
HERE for others to see. Nicely done drawing, by the way.
I have seen these things, though I'll be darned if I remember what they are called. I believe that they can be found in the special fasteners sections of Home Depot, probably Lowes. I think they can also be found in your local ACE Hardware store, in those stacks of shallow pull-out trays that contain every weird part in the world - I love those trays!
Anyway, you should be able to find them without too much trouble. Your drawing is good enough that you could print it out, take it to the store, and show it to the hardware guy! He will recognize it.
Bill