OK Everyone, I finally got Tunisian insurance for my moto. For the benefit of anyone else who needs to do this in the future, here is the process I followed:

1) Insurance for foreign tourist vehicles is not offered by "regular" insurance agents, of which there are many in Tunis. After visiting several agents, I was directed to go to the head office of "Star Insurance", which is located at Devant Galerie 7, Avenue de Paris. This is right in the heart of downtown Tunis. It is a very big office building, impossible to miss.

2) You must bring the following with you: Your passport, the green "Authorization de Circulation pour un Vehicule Automobile" that you get from Tunisian Customs control when you enter the country, and the ownership (registration) document from your home country for the vehicle.

3) In addition to the usual questions, the insurance company will want to know the horsepower of the vehicle. Google this ahead of time so you can answer the question.

The insurance company will only issue insurance that is valid for the duration of the time period permitted on the "Authorization de Circulation pour un Vehicule Automobile". Typically, this will be 3 months.

The "basic insurance" that they provide includes, in addition to liability, some coverage for fire and explosion and coverage for injuries to passengers (not to the driver). The cost of the fire and explosion and injuries to passengers coverage is peanuts (total about $4 USD), so there is no point in trying to get it removed. But, be careful to not over-declare the value of your vehicle. I declared my 2001 Honda ST 1100 as being worth 1,000 Tunisian Dinars (about USD $400) - if I had declared a higher value, that additional coverage probably would have been more expensive.

4) The actual cost of the liability insurance coverage is quite low, about USD $15 for 3 months. But there are a whole bunch of other charges applied - most of which I think are taxes of some kind - and that brought the total cost of 3 months insurance to TND 104 (about USD $40). You have to pay in cash (TND). There are lots of ATMs around where you can get cash.

The process is not fast - it appears that the Tunisians are not as experienced as the Moroccans when it comes to processing tourist vehicles.

In a perfect world, one would be able to buy insurance at the port where the ferry arrives. It is possible that there are insurance vendors at the port - but my ferry arrived very late at night, there were only about 25 cars on the ferry (coronavirus worries, off-season for tourism), and I could not find an insurance office at the port that was open for business.

Hope this information helps someone else in the future.

Michael