I was a member of FIRST teams in SE Michigan in High School. I know that most of the teams in this area have already set up their teams for the year. But if you are looking to become part of a new team I am afraid that you are going to have to do the legwork... you will have the best chance if you call teams and see if they will be able to let you participate. I would start my search for teams at the FIRST site, it lists all the registered teams for this year. You are going to have to take what this site gives you and look up contact info from there if you are really interested.
Go to
http://www.usfirst.org/robotics/resources.htm and click on the FIRST Robotics Event Locator in the top right, click on michigan then click on what are the teams from this state.
Hope this helps.