Yes definitely as Jen said- in case you don't have them:

agdirect.com
horsetopia.com
dreamhorse.com
equine.com
horseclicks.com (still a new site but you might find something)

AND Ask -ALL- the questions you really need to know before making the trip. Not everyone is honest, but it's worth at least asking in the case that they are. I make a mental list of everything that is Mandatory for me to buy so-and-so's horse, and everything that is not of a concern (and ask the mandatory ones for sure before traveling) such as:

Standing still while mounting. (I can train/fix that issue so it wouldn't be a bother)
Neg coggins. (The disease is almost wiped out, coggins tests are not accurate so I at least just make sure they've got a regular temp. and any other horses they have do have current neg. coggins)
100% Sound and healthy (Mandatory)


I hope that makes sense... makes it a little easier! Let us know when you find something