For anyone wondering where to find this weapon, you don’t spawn with it nor is it given to you. You have to pick it up off a dead enemy’s body which i have described below.
Keep an eye out upon entering the compound and you will notice an enemy with a flamethrower, simply kill that enemy then pick up the gun which has the flamethrower attachment and continue through the compound and you will get 10 kills quite easily.
Hope this helps! If i can make this any easier to understand please let me know as this is the first guide i have written.