Here are some options for places that you can request a table and chair when taking part in a tea ceremony in Japan.
I’ve written this as I understand that not everyone is able to sit or kneel on the floor.
Please note that I haven’t tried these companies personally but I do know that they offer a seat option.
I will add to this list as I hear of more options.
Camellia Tea Ceremony in Kyoto
Chazen in Tokyo (Asakusa or Ginza)
Please see here for options for experiencing a tea ceremony in Japan with children.