Nah, asteroid is not enough. you'd need to wiggle a couple or more large black holes in super close proximity. But who knows, may there be alternatives we are not aware of? Is it Higgs boson that gravitational field carrier particle , similar to electrons for EM field? Maybe there is a way to mass-produce those and modulate gravity waves that way, eh ?

In principle, almost anything: any system of masses will emit gravitational waves with an intensity proportional to its mass quadrupole moment (which may be 0, as it is for rotationally symmetric systems). But the proportionality constant is extremely small. Realistically you're looking at stellar-mass objects, if not larger.

Hopefully we build a small transmitter and experiment with it, now that we have a receiver