While I was wandering on Youtube, I've bumped into a channel with a very cool concept.
It's called PostModern Jukebox.
On this channel, the singers and musicians rework popular songs into vintage genres.
If you don't want to spend time searching for actual vintage music for a speakeasy scene, or simply if you want to surprise your players, it could be worth a try. And there are a lot of different styles and eras available.
Link to the channel :
A few sample. (My favourites so far)
Seven Nation Army - New Orleans Dirge
Mad World - Vaudeville
Somebody I Used to Know - 40's Big Band
An example of a less vintage era :
Oops!... I Did it Again! - "Marilyn Monroe Style"