I could be mistaken, but my feeling is that most owners have 150-200 points. There certainly are owners out there that have 600 or more, but not a lot, comparatively. And remember that most owners use their points themselves and don't ever rent out points.
I think your chances of finding a single owner with 600 points who's willing and able to fill that reservation and is working through a broker are very small. I imagine a broker would approach that by looking for two owners who could fill separate 300 point reservations; I don't know if they'd break it down further than that.
No matter how you break it up, it's still a *heck* of a lot of points to find at once.