Check out Mr G's.
Mr. G’s Enterprises Automotive fasteners, of all types
5613 Elliot Reeder Road
Fort Worth, Texas 76117-6013
817-831-3501 or 817-838-3131
https://mrgusa.com/Even if you don't get the clutch heads, he has every oddball type of fastener you can imagine. His website is also a good reference to identify oddball fasteners and clips, etc. If you can't find them in his catalog, give him a call. He's pretty helpful.
His catalog pages will print out with the fastener profiles and heads in actual size so you can lay your existing part over the picture to verify correct fit.