Well, I think you probably have it narrowed down. All of the suggested contenders seem to be necked up or down variations of the good ole 30-06. (.25-06,.270,.280,.338-06, .35 Whelen) Do like they do in the Olympics, throw out the high and low and take the average, you end up right back at the 30-06.
Seriously, while on the road, you can stumble into almost any gas station, bait shop, quickie mart, etc. and buy good 30-06 ammo.
Good luck!