This was an interesting experiment on the part of NBC during the 1964-1965 season. You can read all about 90 Bristol Court in my latest article:
90 Bristol Court was the umbrella title for three individual sitcoms–Karen, Harris Against the World and Tom, Dick and Mary–all set at the same apartment complex in California, with separate casts and story lines. Guy Raymond appeared in all three shows as Bristol Court’s handyman. Broadcast for ninety minutes on Monday evenings, 90 Bristol Court ran only thirteen weeks before two of the three sitcoms were cancelled. Only Karen, starring Debbie Watson, survived the entire season.
Critics really hated the show, although some were fond of Harris Against the World with Jack Klugman. As far as I know, a few episodes of Karen are circulating among private collectors but I’m not aware of episodes of the other two sitcoms in existence. I haven’t created a status guide for any of the sitcoms, so I’m not sure if episodes can be found at any of the big archives.