Well in the most recent issue of Famitsu it has been confirmed that there is a version for the 3DS. Here is some details of the game.
Monster Hunter 3G is an enhanced port of Monster Hunter Tri.
3G is out in Japan this year in Japan.
Will have 12 weapon types and will feature the underwater hunting from Tri.
Local Multiplayer included but online specifics not mentioned.
Touch the touch screen to automaticly face the monster.
New cover Monster is Blakidos.
Pretty excited about the 12 weapon types and that under water hunting is back.
These are the weapons that will likely be in this game. sword and shield,dual swords,Long sword,Great Sword, Hunting Horn,Hammer,Lance, Gun Lance,Bow,Switch Axe, Light Bowgun and heavy bowgun.
Oh also TGS is next week so maybe we will get more info and screens and maybe video of gameplay.