This is a question I got asked recently and I thought it would make an interesting blog post.
Firstly, what is Vaporwave music?
I am not aware of any good royalty-free vaporwave music to be honest. The reason producers create and sell royalty free music is to make an income and you can only do this if you own the copyright of the work you create. Vaporwave is based on samples of older electronic music or sounds that are still under copyright, so the possibility of selling it is a legal nightmare for royalty-free music / stock music creators and producers. I am not aware of any in the major stock music libraries or music producers creating this genre. There is a current trend to downgrade Lo-Fi music to give it an aged effect, but this is not quite in keeping with Vaporwave as Vaporwave relies heavily on manipulating old recorded material such as the digitised Kmart tapes on the web.
Adam Neely explains this in much more detail that I ever could, so please enjoy his great YouTube video.