There are red, green, and blue lasers out there but i can't find a white laser? how hard is to make one? Is it possible?
Its not hard- it bends the idea of what a laser is. Lasers have a single (or very narrow) wavelength of light emitted. There is no "white" wavelength- its just what your eye perceives from a (relatively) full spectrum of wavelengths.
This is generally considered by the scientific community to be an advantage, not a disadvantage. You can do many cool things with a single wavelength that you can't do with a broad spectrum.
You could potentially make a white-ish laser by syncing up many different lasers to make a combination beam that your eye perceives as white. This would be a very difficult engineering problem though, if you actually wanted a spatially coherent laser. Thanks to OpticalResonator for pointing out some folks who managed to do it in a single crystal, which is pretty wild.