You can run into really interesting stuff sometimes crusing the 'net or
googling.

The owner of this website captured some of the sounds for Seabiscuit.

You can listen to some of them here & read about how he got them here:

http://www.robnokes.com/seabiscuitsfx.aspx

"Spring 2003, Nokes recorded race horses at six race tracks for Seabiscuit."

Some of them were made at Turf Paradise and Rillito. Interestingly
enough, he evidently got the starting gate sound at Rillito.

"Rillito was an absolute jackpot for sound, the background noise was quite
low, the outside rail was close to the horses, the starting gate was solid
steel like the old days, and the people were fantastic."