S4B 2013 download for O365?

Hello, We just migrated to O365 and we can't use S4B 2016 because of a Mitel Mivoice Plugin. Can I download 2013 instead? If so, where? I found that I can turn off the 2016 download but I can't seem to find the 2013 download link. I could google more but I'm hoping someone will know the answer for me. TYIA