You have to ensure that any information you purchase regarding the maintenance of (pretty much anything modern) is in line with current company revision status. You can buy outdated company Manuals/DVDs/CD-ROMs pretty much anywhere but there are many problems with this.
i) Outdated manuals contravene Aviation Authority regulations for signing off maintenance on said components etc
ii) DVDs and CD-ROMs often block the user when they have run for over one year so that you have to have the current copy to access the material.
iii) You have to be very specific over exactly what you want.
Best of Luck
001