Restoration Specialties Catalog : page 165,
CLUTCH HEAD SCREWS & ACCESSORIES (a few more items are on pages 170 and 171). All are listed on page 217 in the INDEX. A search on "clutch head" finds them all.
Restoration Specialties' catalog is worth having on-hand because there are correct-sized drawings of all parts, allowing you match parts. The catalog is in PDF to allow correct sizing/matching of parts.
Classic Parts of America (Chevy Duty) has
a few clutch head bolts. (search on clutch)
LMC has some (search on "clutch")
