Tina, I think if I were you I would start at the National Archives of Norway - you'll find their address at the end of this page [www.warsailors.com]
I think it's better to send them a regular letter, rather than an E-mail.

The difficulty, of course, is the uncertainty about his name, but you could tell them everything you know; give them the name Kristian Gundersen as well as Cyril Addison and his birthdate. If he sailed on other Norwegian ships, even under the name Cyril Addison, and even if he was British, they will have a list of them, with the dates he signed on/payed off. It's a shot in the dark, but you have to start somewhere, then go from there. If he did sail on other Norwegian ships, they will all be listed on this website.

Regards Siri
(warsailors.com)