It can be a challenge just finding local musicians that play something that isn't metal or indie. Best places to try are Joinmyband.co.uk, Bandmix.co.uk & Gumtree.
I was searching for ages for Acid Jazz/Breakbeat musicians. I've ended up with a metal guitarist & another guitarist who's taken up drums (& is now the drummer), a house DJ to play decks & sing & another guitarist to share the vocal duties & play some keys.
Man, it's hard work. But I'm sending them facebook messages with youtube videos for stuff like Incognito, Miloopa, Jamiroquai, Groove Armada & so on to get them listening to what they've offered to play (what we end up with may well be completely different, but it'll be fun).
So you might have to find a couple of musicians who aren't Jazzcats & teach them what they're missing.
Maybe check with some of your existing band members & see if any are interested in the Jazz side. Drummers usually are (let them hear some JoJo Mayer & see how things go).
Good luck with it.