Information you may be interested in – shamelessly cribbed from Ed Holmes (with his permission of course)

As some of you may be aware, the famous ‘Envelopener’ that we use for cutting paper, is no longer manufactured.  As the blades in these nifty little cutters are custom made, once they go blunt, you’re left with no option but to dispose of the cutter

Shai, from Origamisrael has created, what I believe, to be the perfect solution.  A 3D printed cutter, that uses a standard #11 X-Acto (craft knife) blade.  These blades can be bought relatively cheaply in packs of up to 100, so you’d never have to buy a new cutter again, just simply slide it apart and fit a new blade when required, just as you would with a regular Stanley Knife (box knife).

3D Printer Files: https://www.thingiverse.com/thing:4689685