The National Theatre has an excellent site dedicated to the posters created for the theatre dating back to the 1960’s. You can browse via genre or decade and the posters are available at multiple sizes for purchase. I recommend checking out the 60’s and 70’s first.
I’ve had this saved in my “links to blog” folder for a while now and I think it’s time to share this gem with everyone else. I forget how I found NAGO but it’s basically a large archive of graphic design work coming out of the Netherlands. The archive contains a lot of great work that you can get lost in for hours. It’s a visual gold mine.
If anyone has anymore info on this site, let me know.