The MG download server has an archive.
For Messenger downloads, the format is https://download.messengergeek.com/version/language/file.ext. And https can be changed to http if desired. 8.5 is listed under 2008.
Some examples:
7.5 Greek: https://download.messengergeek.com/7.5/el/escargot-msn-7.5.0324-el.msi
8.5 English: https://download.messengergeek.com/2008/en/escargot-wlm-8.5.1302-en.msi
Messenger Plus! files are in the msgplus folder.
MsgPlus-4.83.374.exe: https://download.messengergeek.com/msgplus/MsgPlus-4.83.374.exe
MsgPlus-3.63.148.exe: https://download.messengergeek.com/msgplus/MsgPlus-3.63.148.exe
Stuffplug files are in the stuffplug folder:
stuffplug-3.0.387-beta.exe: https://download.messengergeek.com/stuffplug/stuffplug-3.0.387-beta.exe
stuffplug-ng-3.5.590.exe: https://download.messengergeek.com/stuffplug/stuffplug-ng-3.5.590.exe
Other materials are in the escargot folder. For instance
msidcrl.dll: https://download.messengergeek.com/escargot/msidcrl.dll
Escargot-Autopatcher-1.2.exe: https://download.messengergeek.com/escargot/Escargot-Autopatcher-1.2.exe