I was thinking more along the lines of outside research or magic/artifacts, but in retrospect that's hard to narrow down, and from a plot standpoint, it'd be easier to have him question the people at the other ends of those bonds at some point.

Speaking of, can he in turn use those bonds to track down Gil et al, the way they can use them to find him? I've been assuming that's the case, but just to make sure. Also, he won't be able to detect any bonds Raidou has with Infiltrators, e.g. Sabetha, will he? Or will he? Also, will it allow people who are bonded to Raidou to track him down if he's using The Gap Between Images?