No-one else had made one!
Literally. Search google for 'scalpel blade remover' and all you'll find are hard to get commercial products designed for vets and operation rooms, and a single PDF detailing a custom Iranian-made all-milled aluminum one.
I liked the function of one of Swann-Morton's blade removers, whose design I copied slightly.
see the #4 blade remover here: https://www.thingiverse.com/thing:3662179
Demo here: https://youtu.be/_nXSNCWAtyw
This design should work with any blade designed for #3 handles (including the extremely big SG3), and any type of #3 handle.
IF YOU FIND A BLADE OR HANDLE THAT THIS DOESN'T WORK WITH, TELL ME!!!!!!!
I'll do my best to adapt my design to make it work.
3mm diameter hinge pin
cut a 20mm long piece of 3mm rod, or use an M3 screw and nut to link the two pieces together.