FYI: Potential source of grammars on Grammar Page of "Synalyze It!"
This could be a useful repository of grammars (potentially able to be converted automatically):

 * [The Grammar Page of Synalyze It!](https://www.synalysis.net/formats.xml)

There doesn't appear to be any associated licensing information but the page includes the comment "grammars are mainly intended to be used with Hexinator and Synalyze It!".