Here are my suggestions so hope this helps:
YouTube- some racetracks do put up replays but not all of them
ADW/Online wagering website- Twinspires I know does race replays but then again depends on who you are betting with and if they charge for race replays
Attheraces- A diamond in the rough for watching race replays then again hoping that your track is listed on here as they do carry only a select few racetracks but still quite a few for FREE
Hope you can find what you are looking for! Good luck!
