Between my lack of experience and lack of proximity to Michigan, I can't help you directly with the inspection but I can contribute some computer-geek powers to the cause.
You can go into the member listings here:
Airstream Forums - Members List
Then choose "Search Members" and then "Advanced Search" to search for people with specific parameters. I was able to select Michigan and check the "Inspect Trailers Only" box and get several names. You'll want to do multiple searches (one for trailers only, one for trailers+motorhomes, because if you check both you'll get no results.)
If the trailer to be inspected is near a border with another state or Canada, you may want to do a search in the neighboring area. You can send private messages to the people who turn up in the searches as having inspection experience.