So far we have three data points, all of which are for two bodies. However - join the two bodies by a string. Then you've got one body that isn't massively different from a system we've spotted emitting gravitational waves. More seriously, the source term for gravitational waves is a time varying quadrupole moment - so in principle a dumbell or a rod spinning will produce them. In practice, to produce detectable quantities of gravitational waves you're going to need stellar masses, and we don't have any materials strong enough to avoid simply collapsing into a near-sphere under their own weight at that scale. So I think all detectable sources are likely to be two-body sources for some time to come.