Short answer: You can't!
From the FAQ:
"Foldscope is not yet commercially available. Foldscope is a project out of Prakash Lab, a research group in the Department of Bioengineering at Stanford University. We are working hard to make the microscopes commercially available via a spinoff/startup while keeping the mission and our goal aligned to the big vision from our viewpoint. More details of the same will be posted here at some point."