How to use oslc to query requirements by a graphical requirement type

I'm trying to write a script that filters requirements by type.  i've figured out how to do this for text requirements by getting the services.xml document and enuerating the creation factories.  This give me the uri of the requirement type instanceshape (and its name).  So in my script I can say find all use cases for example by finding the instance shape URI and adding that to the query capability as an oslc.where clause.  But I'm stuck on grahical requirement types.  How do I find the URI of the instance shape for these.  They don't appear in the services document for the project area.
Thanks in advance