Where are Visio's "document" stencils
 

I have a Visio diagram that has a set of stencils identified as "Document Stencils", which contain some custom stuff as well as some generic flowchart shapes. When I open it in OmniGraffle, I don't where to find them: Viewing the Stencil palette shows only the things native to OmniGraffle. In Visio I don't see any way of saving just the Document Stencil as a file I can use in OmniGraffle.

Adding a child object to another object does use the same object.

Anyone know of where this set of stencils are found?