Those just look like some strange black caps of some sort jammed onto Universal brake adjusters. (so much for "original") I recall seeing that Robbie has had success now repro-ing the proper Universal (Corsa, mod 61, 68) brake adjuster black booties. Drop him a note if you need some.
While I am sure BOB already knows what they look like, this link shows what the proper booties look like. They were NOS when I put 'em on last year. It's a high-res snap of a bona-fide correct '68 bike (my white Pog), so blow it up if your browser "shrinks" it to fit screen
Dale Phelps
Montagna lunga Colorado USA
This is now the third time I have seen the brake lever adjuster boots. Anyone know what they really are? BOB FREITAS gray skies in MILL VALLEY, CA USA