All of our seahorses came from oceanrider. In my opinion, its the only place to get them.
Their horses are tank born, and raised on frozen mysis. The biggest challenge in keeping horses is getting them to eat, oceanrider takes care of this in advance!
If you're just starting out, go with mustangs. They're as hard to kill as damsels, and take on beautiful colors.
If you think water should be prisitine for corals, ferget it, thats nothing compared to what you need for horses! Keep your parameters textbook perfect, make sure the tank is tall, slow water movement, 75 degrees, and enjoy these great creatures.