Does anyone know about where to look for an eventing/showjumping horse for sale?

I am looking for a new horse but I don't know where to look. I would like a nice horse. We only want to pay between $5,000 and $7,500. I would like a good, credible site with good horses. The breeds I am looking for are Warmbloods, Hanoverians, Irish Sport Horses, or Thoroughbreds. I would prefer the first 4 but if there is a good Thoroughbred that's fine too.