My auto insurance agent informs me that my US auto liability insurance does not cover me in Namibia.

I booked a rental car with Budget in Windhoek. On the web site, there was insurance available for the rental car itself but no liability insurance. I called the manager at the location and he said they do offer liability for damage to another car but no personal injury insurance.

Does anyone know a solution?

You may need to talk to someone else, perhaps a manager in another location.

What do the other rental company's say?

It looks like many rental company's "include" the cost of "Third Party Insurance" in their basic rates - though some may charge for it separately. I imagine that the car has basic insurance coverage on it already.

I checked my umbrella policy and confirmed with the agent. As long as I purchase the maximum liability insurance offered by the rental company, it appears that the umbrella policy will pick up the rest.