It would be great if you could easily access the ngon polygons of a mesh object from the script operator rather than just the triangles!
There is no precise way I can find to work around this so far. Even using the 3dsmax core interface as there no way to get the INode for a tfObj or even be sure of the face correspondence between a tfMesh and a native 3dsmax mesh.
tyFlow meshes don't store any ngons internally. Ngons are really just tris with hidden, adjacent edges.
If you really want to dive into C# you could get the INode from the core interface based on the name of the object...from there you can do your own MNMesh calcs, sure, and extract ngons.
Ah ha... investigating properties via reflection I can see that tfObj does actually have a member called 'node' where I can get the INode and it's name from - it isn't documented in the tyflow script doc is all.