Caveat that I am not a jazz expert *but* IMO the best strategy is to go to the solid if popular places like Troy Bar Weds/Fri or the paid events at 91 Living Room and keep track of the performers you like, follow them on socials and they might announce when they play at random bars you've never heard of. (There are also more dedicated divey spots like Oliver's Jazz Bar in Greenwich but cover/drinks are still a bit expensive)
