Cutaway posters that are featured in Flight magazine are available from the publishers. Really old or rare cutaways may come as photocopies only, but you can still get them. The entire Airbus family is available from flight, and the A320 cutaway can be seen here:
Airbus A320 Aircraft Profile - Flight Global
You will have to dig around and find out how they can be ordered. I ordered a cutaway poster several years ago by using a phone number in the current copy of Flight International magazine. Have a careful look in a magazine or search the website. I had a quick look at the latter but didn't see anything - I'll leave that to you.
UPDATE: Some useful info on this page:
Aircraft Pictures and Aviation Pictures from Flight Global - Aircraft Pictures and Aviation Pictures from Flight Global
"We are gradually moving the Cutaways over to our AirSpace photo galleries which is an important developmental step in allowing us to offer the Cutaways for purchase and download.
If you have any questions concerning the cutaways and their usage, please feel free to contact me.
Giuseppe "Joe" Picarella
Senior Technical Artist"
[email protected]