We know memories can be extracted from a positronic brain (Data to B-4, Lal to Data). And we know Data (or at least Starfleet) had custody of Lore after his deactivation. Thus it stands to reason that if Lore was aware of B-4, someone in the Federation would've begun a search for him before Shinzon's storyline.
The risk is that positronic brains can also be ...
In the novels:
Specifically with a character named Rhea McAdams - who first appears in the book Immortal Coil. She makes another appearance in the 3rd book of the "Cold Equations" trilogy: "The Body Electric"
IMO: Immortal Coil, Cold Equations trilogy, and the Immortal Coil follow-up (Light Fantastic) ...