I have said this before and I will say it again (until you HR people embed it in their minds): if you cannot find C++ developers, start training people and persuade, let alone motivate them to embrace it, learn it deeply and learn its rough corners.
I have lost counting how many interviews I went through and wasn't the right match for them, but loved my zeal for C++ as they have exclaimed with surprise.
When you get rejected so many times, you say "C++?! why bother anyway?" and you give up and follow a different route, using a different toolset that does not asking for the unimaginable, whatever that is they are looking for, and you get respected for what you can offer to them!
If I had the way to gather all HRs around the globe and ask them all at once what is it they are looking for exactly, it would have saved us all from wasting our time.
The whole situation has gotten way out of hand and needs to end, at last!