Downloads for Cubase SX 3, for Converting Cubase songs (ALL/ARR) into CPR format is available at this link:
Downloads for unsupported Steinberg products:
Use the dropdown menus to download the installers from Downloads | Steinberg
Note that installers for Cubase Elements will also install Cubase LE and Cubase AI.
Also available
Cubase AI 5
https://support.steinberg.de/ISOs/Cubase/Cubase_AI_5.1.1.120.iso.
Cubase AI 6
https://support.steinberg.de/ISOs/Cubase/Cubase_AI_6.0.5.357.iso.