Unfortunately you are not in my neck of the woods. I did a search online for training bands, and I began with one in September in Loughborough. I travel 100 miles round trip, but its worth it, and costs me £12 per academic term to attend. It is helping me play 'parts' as opposed to solo really rapidly and I always feel I've progressed and grown each week as I leave. The vast majority (being a training band) are children with several of us adults scattered in there. It is very humbling when you find a 7yr old can perform their part more professionally than you can! Like you, I play tenor, and there is a 15yr old who is at Grade 5, from the Concert Band (you graduate at about half way through Grade 4) who comes and sits in with me, so I learn tips from him every week while we have a good chuckle at my squeaks, burbles, and losing my place so looking at him with my "what bar are we on now?" face. He also shows me any new notes that I haven't achieved yet when a new piece of music is put in front of me.
Maybe a search online for your own area will bring up something appropriate? Don't worry that it may not be a jazz band initially. Any opportunity to learn to play alongside others in a way that compliments, harmonises and produces the whole sound will be rewarding at this stage. Then you can search for your real desire and musical tastes when you feel ready to take that next step up, and in the knowledge that you have developed your 'part' skills.
I'm no expert though, and this is purely reflection from my personal experience of learning to play with others, which is very different from playing alone.
Whatever you do, enjoy it!
Mel