http://www.rondomusic.com/BassLeft.html
^ Scroll down to get to the higher end ones. Some how buying a $90 new bass isn't overly appealing
http://www.gaskellguitars.com/models.html
^ This australian builder specializes in lefty only guitars & basses. They have a remake of a Rickenbacker that may be of interest for some.
http://www.adirondackguitar.com/lefty/lh_bass.htm
^ Scroll down, these guys have a huge selection.
Anyway, if there are any other sites, please list them in this thread.