Most of the fighters you listed Brock have pretty decent chins.

Frank Bruno didn't have the greatest chin, but of active fighters...I have my suspisions about:

Alexander Povetkin - Eddie Chambers hurt the guy FFS
Alexander Dimitrenko - he hasn't been touched by a big timeor even an average puncher yet
Nicolay Valuev - Taras Bidenko, Monte Barrett, and probably some other guys have hurt this big dude
NOTICE I DIDN'T LIST DAVID HAYE.....YET
Roy Jones Jr. - NOW, but during his prime he could take a shot if he had to.
Enzo Maccarinelli - He just can't take a shot 3 losses 3 KO's

I have doubts about Cris Arreola's chin but I am wondering if it's just due to poor training.