Unfortunately the standard explicitly forbids that type of adapter because they could be used to plug two USB-A power supplies together. (USB-C power supplies are designed to prevent this from being an issue.) Source: https://plus.google.com/+BensonLeung/posts/UFCHbSDRa2o

That doesn't mean they don't exist - you can find a few on Amazon - but reputable companies aren't making them, so quality is going to be suspect.