If you're looking for libraries that support 2.7 you're in for a lot more work, you'd have to go library by library and figure out when was the last version they produced that supported 2.7. Almost certainly it will be way out of date and depend on other out of date things.

There was no single moment where every library 'threw the switch' and moved off 2.7 to 3.x, it happened organically over about 10 years. A lot of libraries spent a significant amount of time (and code) supporting both 2.7 and 3.x from the same codebase.