To the best of my knowledge, the only way to do this in the current version of Machform is to do an SQL query against the backend database for your Machform installation. I don't have the knowledge to give you any guidance on how to go about doing this.
I'm hoping user management sees some significant improvement in Machform 5 and that some way of viewing users relations ships to forms from the forms side is added, such as who can access a specific form, who created it, etc.