Thanks for getting my hopes up, WWD. That story was never finished (unless you count the animated version on the BBC website). It wasn't ever lost. I thought one of the actual missing stories had been found, like, say, Marco Polo, or Evil of the Daleks, or Fury from the Deep...
And yes, I did know about the novelisation of Shada.
Can't trust The Bookseller's press release, anyway, not the title. Shada was never completed. Footage still exists, though. I have a scriptbook for Shada as well.
And about 8 years ago, they went back and remade Shada with the Eighth Doctor, along with James Fox as Professor Chronotis, and Andrew Sachs as Skagra. You can find it here: http://www.bbc.co.uk/doctorwho/classic/webcasts/shada/