You can probably buy some of the older rolling stock from DB thought.
The Flixtrain company uses 40+ years old IC (intercity) cars - they have no air conditioning and it's really loud inside with open windows, especially so in tunnels. That is the kind of stuff that DB sells.
https://en.wikipedia.org/wiki/Eurofima_coach
Also no real opening of windows anymore, because early onset of https://de.wikipedia.org/wiki/Druckertüchtigte_Schienenfahrz... <- meaning pressure protection against passing trains at high speeds, entering tunnels, and such.
Anyway, in the 80ies they had AC. In Germany, als die Bahn noch kam, regular IC, no matter if 4-, or 6-seat cabin(depending on class), or Großraumwagen. I remember because sometimes I've been naughty and dialed it down a little, after opening the panel at the end of the wagon with a multitool. Non-destructive, OFC :-)
Like this, but without screen, and more buttons.
https://upload.wikimedia.org/wikipedia/commons/b/b0/13-04-29...
I liked to sit on the window, and there was a metallic grille on the underside of the window. With small slits, maybe 2 to 3 cm long, 3mm wide, a few 100 at all? And that blasted right into your face, or your side if you sat upright, or leaned back. Not noisy, just cold.
Different, probably later design, and apparently adjustable.
https://upload.wikimedia.org/wikipedia/commons/5/5c/13-04-29...
In the Nahverkehrswagen (Silberlinge) it was different. They had no AC, just heating. Which you could turn down or fully off with an open lever. Nobody ever did that. Except me :-) At least their windows could be opened by pushing the upper half down.
https://www.360cities.net/image/abnrz-silberling-nahverkehr-...