I know this reply is over a year late, but if you have any more of those 42-5 bobbin cases/hooks I would love to buy a set off you.
My Singer 42-5 came with several hook/bobbin case assemblies. The hook part# is 13268, which I did not see in the parts list. The bobbin case p/n is 13258. I'll keep one extra for myself and am willing to part with the rest for those who need one to get up and running.