Both Woody and I gave link_s to Restoration Specialties.
You will have to download their catalog and look for "clutch head" (or, go to page 176)? Did you check out their catalog? It is an excellent resource for all sorts of small parts, trim, and misc installation items? Their paper/hard-copy catalog (and pdf images in the down-loadable catalog) are properly scaled, so you can compare your parts to a correct-sized image.
Go the the Classic Parts on-line catalog and search for "clutch". Clutch head bolts are the first four hits.
The other vendors also sell a few styles of clutch head bolts.
I cannot remember if Chevs of the 40s is in the posts I listed. They also sell a few styles of clutch head bolts.
You will not find a source, however, for all of the original clutch-head styles.
