You will either have to buy it (many Poser stores on the web), make it, or contract with someone to create it.
For Poser stores there is ContentParadise, DAZ, RuntimeDNA, VanishingPoint, Rendy, etc, etc. Google is a handy program.
How to make it? If you are a newbie it would probably be best to buy a scorpion from somewhere and learn about geometry swapping, thus swapping scopys head with another head. It wouldn't be pretty but it gets the job done!
You could learn how to model and rig and create from the ground up but that is a task learned over some months, if not years.

Others will chime in with ideas too I'm sure.

Hope this helps.

Comitted to excellence through art.