As far as I know, you cannot purchase the injection mold version of this part on its own, only with the rest of the Q2264A Pen Stall, which retails at around $200 (if you can even find it). While this part does not replace the whole assembly, it can replace the little plastic part by the spring that seems almost engineered to be easy to lose. 

This part is 3D printed in ABS oil based plastics, then sanded down to remove excess supports needed during the printing process. As of now parts are printed in bright red, so as to be more difficult to lose.