When I Was Last In London,

amongst other places I wander around Knightsbridge,

 and stopped at a few shops selling prints or pages from old books or magazines for wall decoration, so for a retro man cave how about using some of these?

these are from a book, The Design of Diagrams for Engineering Formulas and the Theory of Nomography, and are really works of art in themselves, putting aside the actual scientific theory behind them they look so retro, and of course they are, the book was published in 1923, you can see the book expanded here, 

and in case you are wondering Nomography is with today's computer modeling a lost art, but all is not lost as here is the easy to understand explanation of The Lost Art of Nomography.