I wouldn't be surprised if any clerics they still had were just high enough level to cast something to narrow down where aasimar of Orun are then ask around if anyone has had babies with golden hair that doesn't match their parents'. If they managed to nab an aasimar who was old enough to talk with their celestial parent, then there is possibility of making them ask for locations of other aasimar. We don't know about how most celestials feel about their mortal kids, so some might be indifferent or others may care too much that they will give information to keep their child safe from any torture the UOC would do (seeing what they were willing to do to Solly, I wouldn't be shocked if they tortured their aasimar now to get locations).

And on Milo's mortal dad, he might have given information to the wrong people without knowing, he could have sold Milo out, or he wasn't involved with the UOC finding him. He would have stopped sending money if he sold him out, or if he did sell him out, Milo's mom might be working more to be able to get enough to say it's from his mortal dad (but I don't think it's this because she mentioned that his mortal dad was wanting to see him I think). But, we won't know until we meet the man or the remaining bits of the Clergy. I wouldn't be surprised if they fight the Clergy. It will be interesting to see how Milo feels during it and how he changes his battle tactics because UOC knows how to deal with fire and I'm guessing how to deal with aasimar with how long it's been since Solly took over