The Lost Expedition - no map drops

I have leveled 2 characters past 40 (71 and 43 as of writing)and done 150+ expedition events, however, not once have I had the book/map drop in order to continue with the quest.

I am basically cut from 50% of the league mechanic.

they are rare, I got only one so far..

not sure about what 50% of mechanics are you talking about. they are just a big excavation sites with extra stashes. similar to blighted maps

you can easily get one here: https://www.pathofexile.com/trade/search/Expedition/VYGmJRXIp