According to Peter McConnell (
http://www.lucasarts.com/products/grim/grim_spotlight.htm), at least two tracks were inspired by Duke Ellington, so his music might be worth checking out. Since it's so old, it's in terrible quality...but after listening to it for a while you don't notice as much.
He also mentions the Benny Goodman ensembles, so maybe take a look in that direction too.
I'm too lazy to dig up a bunch of similar-sounding bands, but still hope to have helped.