You can get a 2d representation of the perimeter fairly easily with a few nodes from Clockwork. For a 3d boundary, I’d have to go with Konrad’s suggestion and go with Grasshopper.
As a free alternative to Gh/Rhino, you could try Blender. You’ll have to extract the topo’s mesh and then export the file as an *.stl (make sure that only the topo mesh is visible in the background preview)
You can then import the STL(you might need to change the units in blender prior to importing), go into edit mode and select all non-manifold geometry:
Getting the data out of blender might be trickier tho…It has a ton of export plugins available and you’ll have to figure out what best works for you…