I found an old DVD - well, obviously an old documentary converted to DVD - about Nijinsky for around $2 on Amazon. It looks like it was filmed in 1970, all sorts of footage including interviews with the trainer while the horse is standing right there. Gorgeous looking horse, too. Beautiful head and alert expression, though he looks nothing like Northern Dancer. This was well worth my $2.
I got to wondering about Vincent O’Brien, Nijinsky’s trainer. The yard, presumably the same one, is called Ballydoyle, too. Is Aidan O’Brien a descendant of his? Pretty common name, but to have two O’Brien’s training in an identically named yard is a coincidence if not a relation.