Squadron has a pretty decent supply:
http://www.squadron.com/
Then ther is also internet hobbies:
http://www.internethobbies.com/internethobbies/index.html
And Eduard:
http://www.eduard.com/
And GreatModels:
http://www.eduard.com/
Those are the ones I typically browse, but each website has links to other sites that you might want to consider as well.
Good luck!!