Fwiw, we did a 13,000+ mile road trip in our VetteVert, two summers ago; it has non-RFTs, and no spare, of course.
I simply packed a small cig plug outlet compressor, a couple of vise grips, a good plug kit and didn't give it a thought. No flats, no prob, and the average small town tire joint is not stocking tires for the Vette, either.
While not answering your question directly, and considering your option(s), I feel that buying a another set of rims/tires for drives beyond the reach of a dlr or big tire store is an extreme measure.
And, your 'average to good' tire joint may not have your oe size tires in stock, anyway. Same goes for an given BMW dlr.
I have made that run across KS several times, and while western KS isn't metro KC,MO there are several towns all within <50 miles of each other: Abilene, Hays, Colby and then a fairly empty run climbing up to Denver, but not a huge distance, which could provide a shorter limp in if absolutely necessary.
But, if I was a 'ways out', I would plug the sumbitch and keep going to a metro area and a better chance for replacement.
Even a RFT tire is pluggable, to get you down the road to a metro area...I wouldn't wring my hands over the trip.
And, when was the last time you had a flat, on the road? I thought so...
My 50Cts.
GL, mD