There's a couple of things in the Minneapolis area.
There's StrumMn which gets together once a month (usually a Sunday) at the Pavilion in Como Park in St. Paul. They play a lot of old time stuff.
And I've been working towards assembling a Twin Cities Ukulele Orchestra which is going to have its first meeting next week (Feb. 25th 6:30pm) at Java J's in the warehouse district. How that works remains to be seen, but I hope that it will at least be fun. There's some files up on the forum should give you an idea of what I'm shooting for.