Just a thought....
Even if you cannot carry a spare (due to 3rd row of your car doesnt have a location)...having a spare tire AT HOME in the garage can be a great strategy for dealing with a flat.
1. On a long trip, if you arent using the rear seat, you can toss it in.
2. If you get a flat locally, a family member can drive it out to you. (Instead of getting flat-bedded to a tire store, and having to buy 'the closest they had in stock'.
Next time you get new tires, keep the one with 'legal tread'...then hunt for a one-off rim in classified....
FWIW.
Regards,
Mr. Belt and Suspenders.