Grain Edit is a fantastic blog that focuses exclusively on classic design work from
the 1950s-1970s and contemporary designers who draw their inspiration from
the time period. I never thought you could find enough work inspired by a measly
30 years but they do, and succeed at it.

I really like this post about a rare book of Russian posters from the 70s,

This one on Polish book covers,

and this one on Bulgarian designer, Stefan Kanchev.