The only airside UnitedClub Las Vegas is the old Continental Airlines President's Club, following the closure of the United Airlines Red Carpet Club (although there is also another lounge in the international section). Unfortunately this lounge is in Concourse D, which you can't access from any of the A/B/C gates. On that side there is just no lounge available for you at all, and you'll be stuck with either playing the slots, or the Irish pub.