What? How?
Silicone molding is a simple method to create molds that will help reproduce products efficiently. You can either buy a two part mix to make the mold or make it out of some household items and silicone. You can also buy pre-made molds for shapes you might want.
Do It Yourself Method
http://fallfordiy.com/blog/2014/04/27/how-to-make-a-silicone-mould/
http://www.instructables.com/id/Worlds-easiest-silicone-mold/?ALLSTEPS
Where to buy?
You can buy silicone mold mixes from a range of places including inexpensive art stores or more expensive but stronger molds from online suppliers. Below are a few examples:
https://www.michaels.com/easymold-silicone-putty/10184918.html
https://www.amazon.com/Cast-Mold-Silicone-Rubber-Gallon/dp/B008UVMWKC