There is an old saying in the newspaper business, "Freedom of the press belongs to those who own the press."
As previous posters have stated, a newspaper has no obligation to publish opinions contrary to those of its editorial writer(s). Many will, in the interest of fairness, to present more than one point of view to their readers, or just to create an illusion of openness.
You may not get a letter opposing a published editorial printed, but if you don't send it you certainly will not. I have no idea what the newspaper situation is in Kansas City (too lazy to do a search), whether there is any competition or alternative to the Star, but that might be an option to get the pro-2A word out to the public. Not as good as being on the same pages as the Star's anti-gun pieces, but a letter in the "KayCee Free Classified Shopper Sheet" beats heck out of silence, IMO.