I'm sure I read somewhere that at least one person wants the Santa Anita downhill track in SO6- whilst I can't give you that, in the meantime here's the same track for SO5. 've created new wp files and a new course map for this. Its as accurate a model of the santa anita downhill track as I think you will be able to get. Also included are backup files of the original santa anita files, so all you need to do is go straight ahead and replace the wp files and course map.
https://www.mediafire.com/?2n02glwua6pwwa2
N.B Having gone back through my old games that I had before putting this in place it has now changed all races that have already been run at Santa Anita to using this course, so you don't have to worry about it not matching up or anything like that.