These are the informations I have about breeding walrusses in captivity :
The world first breeding of them was May 26,1975 at the Marinleand of the Pacifc in california. The Father, Farouk, fatherd 5 calves with two females at this park, but only two survived.
They got new walrusses, but they never bred them again. In 1987, the Marineland was closed and the walrusses came to Seaworld San Diego. The same year, the female gave birth to a calf, it had to be raised by hand.
1993, another walrus was born at Seawold and raised by its mother.
1991, Cincinnati had a walrus birth also, but the baby died one and a half month later.
The dolphinarium Harderwijk has bred three walrusses, two of them are still alive.
I have no information about walrus breeding in orlando.
At the New York aquarium, last year in june, a walrus was born and raised by its mother.
I don't belive that walrusses are hard to breed, but most zoos are keeping to less of them, they should keep bigger groups.