Hiya and Cheers
Saddly for you, I am but a crayon, 3d Graphics Modeling......made a fair few of the track sceneries...my job was "everything outside the armco barrier" and I got to do Monaco, Canada, Spain and about 10 other tracks, slept on floor of the office on and on for about 4-6 months...eek....lol.........(we had a slight subcontractor problem at a late stage so it was mad time, hence we all had a pile on our plates) I was on the Microprose side, which was mainly graphics and integration of Geoffs (Synergy) code with various platforms, PC: Xbox and PSII (sadly not released on the 2 later, a bit like putting a bowling ball in a marble bag as they say.....
I think I still have Monaco as a 3DS Max file (proud of that one).....and probably have the source .tgas...I think I have Austria and a few others as well? But the graphics is'nt the problem in the mod community from what I gather...
As for the code...well......for that I assume you would need to talk to Crambo.....or Geoff Crammond as he is otherwise known.......but it is fair to say, he is a very special kind of genius and if I was him, I would'nt give it away either...lol.........
Have'nt heard from him in a while in the games industry and have no idea what he is doing now, but his physics and code is pretty legendary and so I assume, closely guarded.
My job was to screw over all of your machines and graphics cards by adding everyting I could see in the reference photos to the 3D Models......... But it did look pretty, and it ran too....5 years later on better machines.....LOL....
I'm no programmer , sorry.....I don't break your machines, I just grind them to a halt..........;)
Edited to Add: If codemasters has any sense, they will be knocking on Geoffs door.......