The other site that 'Toon' recommended was Dads UK, which describes itself as "a news and information site dedicated to giving a voice and support to all people interested in fathers' rights". There doesn't seem to be an awful lot on the main site, but Toon recommends the forum, which he says "provides support and advice to dads going through Family Law hell". I can't comment myself, as I haven't registered for the forum and it can't be accessed, even for viewing, without registration.
Only one thing I would say about all fathers' rights sites and organisations: what about all those mothers who are denied contact with their children? I know some of these sites/organisations provide help to mothers too, but a lot of mothers will be put off by the word 'dads' or 'fathers' in their names.