In reply to nutme:
Individual Councils in Scotland keep records of all approved public tracks and paths that are "reasonably accessible" to the public under the Core Paths regulations. Unfortunately as far as I am aware there is no coordinated Scotland wide version, and you have to access each area of interest through the appropriate Council.
Most of these core paths are able or should be able to be cycled, but only up to a point (in my experience some have difficult landowners that object to you being there, don't have bike friendly gates, have steep sections, narrow sections, across farmland, wet & muddy sections, for example). Also, apparently legally there is no requirement to maintain them regularly or to be accessible at all times which means some can get very overgrown, temporarily closed, etc.
Have you had a look at
http://cairngorms.co.uk/wp-content/uploads/2015/06/CorePathsPlanFinal150727... and
http://www.highland.gov.uk/info/379/countryside_facilities_and_wildlife/163... to see if there is anything there? You could also contact the appropriate Council Access Officer who maybe able to help?
My local council's Access Officer is very easy to contact by phone and email and always happy to help, and my local Council keeps extremely detailed downloadable maps of all accessible routes and details of diversions and closures. They are all "signposted" on the ground with the small core path way markers en route (though actual use of the online maps is a bit tedious as they are so detailed and are on large(ish) scale maps). Hopefully Highland Council and other Council areas that you intend to visit are similar.
Post edited at 14:51
