How do I find the alien gun?

I'm an avid gamer and have been searching high and low for the elusive alien gun in the latest sci-fi shooter. It's rumored to be an extremely rare find with unique capabilities. I've been following hints on forums and guides, but they've all led me to dead ends. So, how do I actually find this alien gun? Do I need to complete a specific mission? Is it hidden in a secret area? Or is it a random drop from a rare enemy? I'm at a loss and would appreciate any tips or tricks to help me locate this coveted weapon. Any insight you have would be greatly appreciated!