Obtaining a non-digitized thesis I have been trying for a few weeks now to obtain a published thesis (this one, if you're wondering), but have had no luck in doing so. 

There currently exists only one copy of this thesis, at the Lewis Library of Princeton. It has not been digitized. I have contacted the library to enquire about obtaining it, but not being currently affiliated with any university, the best they could offer me was to ask local libraries about inter-library loan programs. I have done so, and discovered that people were amazed that inter-library loans were still a thing, and after ferreting out the person in charge of it, discovered that they would not even consider an ILL from the US (I am in France). 

Are there any other process I can try to obtain a copy of that thesis?
You can try contacting Robert Marzke himself. There is a chance he has a digitized version of his own that he is willing to share.