There are a number of fantastic Learjet flight sim builders around the world that can be found here:
http://www.learsim.com/
http://www.flightlevel180.org/
http://www.learjet45chimera.co.uk/
http://www.lear45project.org/
http://bjay.id.au/wordpress/
http://ninepointeightone.com/wordpress/
http://l45.sytes.net/
http://members.ziggo.nl/j_both/index.html
http://flightsimmersion.com/myproject.html