combine a green and yellow one
lol it would be like 5x more expensive that way
here are a couple of instructables on that.https://www.instructables.com/id/New_007_Laser_Weapon_Revealed/https://www.instructables.com/id/Blu-Ray-Laser-Phaser!/
You could buy a blue laser pointer and modify it.
You cannot literally "make" a blue laser at home, unless you have madd skilz and madd workshop facilitiez. You will need to purchase a gallium nitride laser, which has an output wavelength of about 405nm (a typical red laser is at about 630nm). This is more of a blue-violet, but it's as close to blue as you are likely to get. These are the lasers used in BluRay drives, so if you find a scrapped PS3, that's a good place to look. You can also purchase the laser diodes all over the Internet, a bit of searching should help you find one for sale.You can get more information on how to use the diodes here and here.