handbook?

Depends on exactly for what you are looking. If its towing weights etc., a simple Google search gave this as the first result:

http://www.gocaravanning.com/caravan-specs/Mardon-Caravan-Data.html

This may also be some help:

http://www.caravantalk.co.uk/community/topic/98534-does-the-mardon-owners-club-still-exist/

Anon
July 2016