For the Southern Californian, a protracted loss of Mexican food resources can become a dire calamity. Rest assured that if you're in the birthplace of Harry Truman, you can get good Mexican food at El Charro. It's on the main street just around the corner from Truman's. With luck, you can hear locals wrestle with such linguistic concepts as Pico de Gallo and Quesadilla. If you're long gone, and confused, the menu offers a handy pronounciation guide.
Just a friendly FYI, since Lamar, Missouri is of course conveniently located right beneath the flight path for all you NY/LA bi-coastals.
Also, the enticing, pretty Evanston, Wyoming is host to the smashingly excellent Don Pedro's...should you end up there too on a business trip, or, umm, dude ranch.