User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-190.37.255.158-20111227190304/@comment-70.54.113.166-20111227224229

Tigrex would probably be available already if he isn't. Akantor and Ukanlos could still be possible: at least two monsters were unlocked by raising HR, and many other quests have been unlocked the same way.

I think Akantor was originally available only through download quests (though he isn't actual DLC). Someone else can confirm or correct me.