Founds these on Amazon called: Horizontal Blinds Bottom Rail Ladder Cord Button Plug 1/2".

I noticed that half of all of these in my house were missing because they broke and fell out. I just got my 3D printer a couple days ago so decided this would be my first "useful" thing to build. In the pictures, you can see what the original, broken, ones looked like and the ones I replaced it with.

I changed the design, just because it was easier, and probably stronger. If you would sand and match the color, you probably couldn't tell it wasn't original.