Welcome to the forum.
Are you referring to Photoshop CS 6, or Photoshop version 6 (many years old)?
With Adobe going to the CC (Creative Cloud), you might have to hunt for Photoshop CS 6, and finding an upgrade w/ upgrade price, might be a bit tougher still. However, I would anticipate that there ARE resellers with a limited supply. I also think that most would want to clear out any stock of Adobe programs, because most will be cut out of the supply chain, with the full implementation of the CC version.