Late one night I decided I wanted a fan mount for my RepRap Mendel....here is my attempt..I have not yet made this as my Mendel is out of action due to upgrading the x and z axis to non-simplified...STL passes tests and does not need repair in netfabb though. (Hoping it's strong enough)
See sketchup 3D model or look at pictures to get an idea...you will need lengths of 8mm rod and a 120mm fan..not forgetting the RP parts listed!
(you need 8 of the y bar clamps btw)
Good luck ;)