Recommendations for Photos to Purchase?  

Try reaching out to DSP Photos (Dave) he took a lot of photos at Flemington in the years you mentioned.

Bobby Armbruster did the same at Orange County.

Here is a website that I don't know if it is still being monitored, but there is contact info on it for them and others:

https://nepart.smugmug.com/ 

There are folks that probably have the images you are looking for, but may not have them organized by race, so it might be a little tricky, but hopefully they will be able to start the ball rolling.