Sorry for the delay. I asked for help from a friend that works in the US and apparently that screw only exist in Brazil !!!
There already is an option in the SCAD file for M4 screws, I don't know if M3x60mm screws are available there but I used threaded rods with nylock nuts in place of the screw head.
The only difference between the 2 options is the nut housing which is bigger for M4 then for 5/32" nuts. If you have problems, I can upload a set of .STL files for that, just ask...
If there is a more convenient screw available I am willing to include it as an option too.
BTW, I just assumed that that is an US problem, your profile is incomplete in that aspect.