While the Nintendo eShop is no longer available for new purchases on the 3DS, the game is frequently archived by community-driven preservation sites:
: You can still find physical game cards (product code ends in "USA") at retailers like GameStop . Online Play Status Monster Hunter 4 Ultimate 3DS ROM & (USA) CIA (...
Monster Hunter 4 Ultimate is available as a (installable package for modded 3DS hardware) and a ROM/3DS file (typically used for emulation on PC via Citra). Technical Details for the USA Version While the Nintendo eShop is no longer available