I would not spend too much time as most owners manuals I have seen arnt worth much. I would concentrate on finding a good general maintenance book.
The only thing an owner's manual helps with is the setup of the rigging. And that info can be found online. The manuals I have seen mostly are 6 or 7 pages of info about commissioning the boat in the beginning. Not much more.
I have all the original documents from my mirage 25, the closest there is to an owners manual is the blueprint/sketch of the sail and interior layout, and across sectional drawing of the boom and spreaders. That's about it!