Good grief.
I think Sheincar has done a good thing by bringing the shirt back to Cardiff. It really is that simple. If it were me I'd do the same thing. If it was my child who had lost the shirt I would switch my brain on and try to find out if any hockey fans had any ideas where it might be. I'd go as far and radical as doing it the same day.
If I later found out that the shirt was sold to raise money for charity and my child was devastated I would use it as an example to show them how lucky they are, not chase after the person who did their best.