After the original hook broke I made a new metal hook for my kids' Rainbow Loom.
I made the new hook out of a piece of metal rod that I salvaged from a cooking rack. The new metal hook was installed in the plastic handle by pseudo spin welding it in place using my Gingery lathe. It is not really a weld. It is more of a friction heated interference fit.
I made this a while ago and it has held up quite well.
Here are a few pictures and a short build video.
This is the original hook with the broken part.
This is a finished hook installed in the original handle.
And here is the short build video.
My kids made a little web page showing some of there creations: Fishitales