6 weeks out, it’d be a great race to use as a trial run. Meaning, run it at marathon pace, practice drinking water and/or gatorade (or whatever is offered at Green Bay), taking gels, wearing same shoes, socks, etc. Anything you plan on doing at Green Bay could be practiced for this half marathon.
As for tune-up races, try to find a 8-10k 4-6 weeks out from Green Bay. There’s gotta be something in your area.