Plz Give me challenging design for injection mold
2 Answers

Injection molded plastic part Design
Many, many, many other parts listed on GrabCad, try a few keywords such as:
Molded
Plastics
Injection
etc...
Hope it helps.

Give this guy some help, he just posted this yesterday:
https://grabcad.com/questions/how-to-make-plastic-mould-die-for-this-model