Well it seems the older brother got separated before the younger one got kidnapped. Since he said his mom was with the younger one when he end up alone.
So Shion might have tried to looked for Madoka? but since he hadn't been there for the kidnapping and the SIS people were trying to keep the saved kids safe he probably had zero luck.
You would think that all the organizations they are in would have some sort of networking database or even private investigatorrs that could just pull up the information. The mangaka could have had a lot more gushing fans had the brothers met.
But it seemed to me as if Madoka thinks Shion is dead, and Shion seems to think likewise of Mafoka and his mother
Why didnt the brothers ever meet? Ugh. T.T