I was surfing today and was amazed to find that the British Library have an archive of websites. http://www.webarchive.org.uk/ukwa/ this claims to be an archive of sites which no longer exist. If they are live they give a link to the live site. They do not appear to have any audio or video on the site,but it only started off in 2004.
Meanwhile in America their archive website has been running or many years, it includes web sites video and audio. I recommend the OTR section (0ld Time Radio) It contains many British BBC radio shows, also wartime actuality, Churchill speeches, Lord Haw Haw and much more
A site which hosts a large collection of offshore radio recordings is Azanorak, and I hope that one day this site will be archived. The files are zipped up and have a password which you can obtain by belonging to the Caroline Mailing List on Yahoo Groups.
Finally for this post, building into a rather excellent archive of facts and pictures, and sounds of offshore radio broadcasters, is Pirate Hall of Fame http://www.offshoreradio.co.uk/