I've been using .270 Win for deer and antelope, and now elk (just shot #1). I know some think it's too light for elk, but with a well-placed shot and good bullets (140 or 150 gr Fail Safe, Trophy Bonded Bear Claw etc), it worked fine for me, and for the friends who have taken dozens with .270, and with mild recoil. For me, the next move up from .270 will probably be .300WSM in a Browning A-Bolt, but I agree with those who say that you already have a .30 caliber rifle, so maybe for you, the next best step might be .338, which some hunting writers call the best elk caliber bar none (and of course, ammo can be bought abroad, as was mentioned). I imagine it recoils noticably more than .300, though.
Winchester has just introduced both a .270 and 7mm Win Short Magnum to complement the .300WSM, but I think the .300WSM may be the most versatile. It is a more efficient round than .300Win Mag, supposedly has less recoil, and is a short action caliber (which works ok with a 23" barrel, whereas the .300 Win needs a 26" ideally).
Too many calibers, too little money
ps: I hunted elk this year with my caliber-crazy hunting buddy. I filled my tag a week ago, and he took his elk yesterday. He had both his custom blasters with him... a 7mm STW and a .300 Rem Ultra Mag, and because of the potential for a long range shot and the 50MPH gusting winds, he chose the .300 Ultra. He ended up shooting his cow at about 330 yds (couldn't move closer and light was fading) in a gusting crosswind, so the heavier 180gr bullet was good. BUT-- one round struck the shoulder in profile, and absolutely pulverized it and part of the opposite shoulder. Turned the meat to burger... that Ultra packs such a wallop. Maybe too much?