The first option - no one will admit to left over inventory and probably aren't lying anyway.

The second option is to scour e-bay - something will appear from time to time.  There is someone on using TT that still plays DT Solo with rubber band wrapping instead of a solid core.  ...I do have a 3 pack I found with a logo I recently found if he wants them, probably from the late 80's.  He buys 3 to a dozen as they come up.

Some of the refurbished/used ball dealers may have some.  I know I've seen labeling for 2007-2008 versions for sure.  I'm not wild about refurbished (one driving range uses some where the dimples aren't consistent and will leave white paint on club faces) but I've not had an issue with 4/5 star lots of the couple used ones I've tried.  All surlyn covers, no urethane, which may these easier to recycle.

I'm pretty sure that Titleist stopped making this style of ball when they made the next model of Pro V1x. You might be lucky enough to find some on ebay, but those most likely will be from all different years.  

Stetson please follow this link

Hope that helps

sorry but the link isn't working but just click on lost golf balls.com pro v1/v1x pro v1x 332 and there the 2005 model