To anyone else who finds this older question, you can now download all old versions.
Xcode
-> Preferences
-> Components
(Click on Simulators tab).
Install all the versions you want/need.
To show all installed simulators:
Target -> In dropdown "deployment target" choose the installed version with lowest version nr.
You should now see all your available simulators in the dropdown.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…