There's heaps of supplement blends you can buy, but from what I can tell they're very similar to ones that grow your breasts. Seem to work off the same idea of increasing estrogens so that your body will store fat on your butt. Came across this one called gluteboost at this
better butt challenge website that seems pretty well reviewed (and I think you might like that site as well, it's all about getting a bigger butt!)
Butt-focused exercises may work? That's what I do for mine since I'm lacking in the boob department! That website says the butt is just a muscle, and muscles can be made bigger with exercise. But I think as a male you'd have to be careful with your testosterone, as I have heard that exercise of the larger muscles can lead to a big testosterone release.
For exercise, I have read that squats are okay, but the best butt exercise is glute bridges or hip thrusts, they are supposed to help get your butt more than just squats do!