This font will allow you to type all the characters in the Hidden Valley script. It isn't technically perfect but it's been tested on various Windows PCs and it seems to do the job. If prompted with the options "Open" or "Save" click "Save".
Once the file has been downloaded, right-click the file and click "install" to install the font.
Hidden Valley font for Windows PCs
This pdf file shows the character mapping for the font. Bear in mind that the order of the characters is completely random so don't waste time trying to deduce anything from this order!
Character mapping (pdf file)