I'm in the house band for a jam night. It's nominally labelled a blues jam, but we've had folk singers, a drum troupe, a guy on a didgeridoo and every permutation of 2 guitars, bass and drums. We also get the occasional keys players and a brass section. We've been going for over 20 years and have many regulars. We get serious people but the guys who get most out of it are there for a fun night. The one thing I hate with a passion is a badly played slow blues. . . . and Red House in particular. Jeez, show some imagination!!
Anyway, turn up and tell the guy running it what you want to do. If they are any good at running jams, they'll try to put you together with people who will be able to support you. Of course you can end up with the guitarist from hell, but that's jam nights for you!