Check The Original Game Boy Manuals a.k.a Dot Matrix Gameboy here: DMG

if you can't find it there: be sure to look for Colored Game Boy  Manuals. 

When it's not a real manual but more of a flyer / brochure , please check this section: Gameboy & Nintendo Brochures 

Or Check out the Game Boy Advance (AGB) section over here

or

Take me to the Games!