I don’t think you need a guide, but I would recommend the OS map
The two routes worth doing that I’m aware of are the lollipop (Annat-Coire Laire-Achnashellach-Coulags-Annat) and the loop via the lake over the Ben Damph estate.
Very easy to follow despite it being in completely epic surroundings. There’s a very clear path for 99% of the lollipop route I did, but I did check the map a lot, just to be sure. A wrong turn could have dire consequences but with a bit of prep and good map sense you’ll be fine.
I found this link pretty handy:
http://www.mtbtrails.info/Trail_Venue.aspx?VenueNumber=27