No simple answer as it depends on a number of factors. Who published them (manufacturer or operator) and the condition being the most important. I'm not sure but it seems the folders with performance graphs ought to belong to either the Flight Manual or the Operations manual. As hundreds of these aircraft were made there should be an ample quantity of their manuals about. The price quoted seems rather steep to me especially as you can get them on CD for £20 or less. Try
www.Flight-Manuals-on-CD.Com Ltd in New Zealand if that appeals.