More information on hardware: the nuts and bolts
Studying the STL files out to obtain the dimensions may work. Look at the dimensions and figure out which one is which. Post the found component as a comment.
https://www.mcmaster.com/t-slot-nuts/t-slot-nuts-5/ for t-slot nuts
Springs, Arm-Springs. How to measure? 3D print a reference?
Belts (how to do this? 3D print using a different material?)