I remixed the OTF Knife / Switch Blade by David6722. I really loved the design, however I find that it was often sporadic and every now and then it wouldn't retract. i edited the slider to make it more reliable. I also found the trigger very painful to use and so I made that smoother and easier to access. If you have already printed the original files by David6722 then just print the slider from these files and it should fit right in and improve it.
If you do print this then be sure to post a make and leave any feedback that you do have.
Happy printing :)
P.S. You will have to scale all the files except the slider 10x to get it to fit
Edit: Added a textured version of the slider as per a request in the comments.
Geeetech PLA 1.75mm