The purple laser for gun is 405nm violet purple laser gun sight for pistol or rifles.

You can buy the purple laser for gun here at Beamqlaser for just 89$.

Amazon Ade Advanced Optics HB06-1 Triple Duty 450nm Blue/Violet Laser Sight with Picatinny Mount

eBay Ade Advanced Optics Strong BLUE/Violet LASER Sight for rifle/shotgun with Mount

P3P – Purple Laser Sight
But it seems to be out of stock

SERIOUS PERFORMANCE BOTH ON THE RANGE AND IN THE FIELD – the P3P has a bright purple laser which is clearly visible especially at night while still meeting law requirements <5mW peak, 532nm, Class 3a;
DURABLE AND BUILT TO LAST – made from military grade nylon the P3P is designed to work under the harshest conditions to provide reliable performance time and time again. Backed by a 1 year warranty at HiLight Tactical we stand behind our products;
INCREASED SPEED AND ACCURACY – the included Allen wrench makes it very easy to dial the red dot sight into the distance you want so even when hip firing missing the target becomes a thing of the past;

You can see a violet laser target dot at the following pictures.