I am level 140, and have a sensitivity of 160, almost making the game unplayable. I haven;t found a single desensitize potion, I am playing the Steam version of the game, which oddly has no forum.

You have to buy the recipe from Nemi for 5000 Yen

About the forum, yes it seems for the first game the whole hub disappeared too (no discussion board, guide section, etc.).