Costco itself doesn’t sell the insurance, they just offer it through arrangements with carriers so it has the Costco branding when you start. I believe the carriers are different depending on where you are because not all carriers work in all states and offer all products. So all you have to do Alfred is give them a call and see who deals with it in your area...
At the times I investigated this they were not offering any insurance products in Michigan. In my early years in Michigan, certainly for homeowner's insurance, it was low cost, and steady in price. In the 2000s it started climbing precipitously and then it became a chore each year to shop it around. My homeowners insurance (never made any claims by the way) went up 1000% in the time I was there, with increasing deductibles. The carriers always wanted you to bundle all your insurances together.
On the automotive side, it was once a buyer's choice whether to have a 6 month or 12 month policy. Last we had insurance in Michigan on cars, they would not write 12 month policies, only 6 month such that they could raise them 2x per year. We had one claim on an automotive, due to a hit and run on my daughter. The estimate from the dealer was going to be well over $2,000, and we had a $1K deductible. So, we filed a claim. Turned out the estimate was wrong; it was only a $1,300 repair. We paid the $1,000 deductible. The insurance company paid the remaining $300. Within days we got a notice that they had raised our premium for 6 months by $300. So, they would get back what they paid out twice over in one year...and this would continue for three more years, netting the insurance company $1,800 additional on a $300 payout in addition to our policy's starting cost. Had we known that we would have paid out of pocket, but you can't undo it. Don't hate lawyers. It's insurance companies you should vent your anger at!
Sometimes you just have to give up which is what we did. We moved. There are no such insurance challenges here in NC.