You can find some mods here:
Maususer's site: http://home.comcast.net/~jmaleski/my_mig_alley_page.htm
Mods by Viper, Axa and others:
http://users.telenet.be/johan_eaf274/downloads/migalley/These make some aspects of the game look slightly better, but there won't be any spectacular improvements as in better clouds, 3D models or more detailed terrain mesh.
Then there is the unofficial Mig Alley 0.85F patch:
http://www.simhq.net/downloads/air_combat/mig_alley/BDG_MiGAlley_085F.zipThis doesn't improve any graphics, but introduces 6DOF TrackIR support and adds some much needed stability and other bug fixes.
After all these years Mig Alley is still one of my favourite sims. It can be most frustrating due to some bugs and CTDs, but there are times when everything just comes together beautifully and then it is brilliant.