Microsoft provides 18 months support of each Azure AD Connect version.
Sometimes, it is useful to download old Azure AD Connect versions to perform migration test or someting else.
Microsoft allows you to download only the last Azure AD Connect version. Find below all the old Azure AD Connect versions (msi) I have.
PS : It’s not directly related to Azure AD Connect, but if you love the ‘old’ version of everything, you can find Technet Gallery scripts here.