Going to Sunshine, Oliva or Villamoura is actually really good advice without having existing contacts. Walk up to the rider after the round and ask if the horse is for sale. This is commonly done.
If you spend a week at one of those locations you should be able to try a bunch and also see how they do at a show environment. Yo may not get the bestest price as you would if you went straight to the small breeder that campaigns locally but should still totally fit into your budget.
Have one of the vets there take the films and send them to your own vet for review. I’m sure it still happens but I bet those vets are less likely to collude with the seller than their local vet would.