A few of my clients use these commercially and wear out the heads so for ease of replacement I have created a silicone mold so as to cast up a more durable version.
Put the two halves together and either clamp them or put rubber bands around them.
Pour in your choice of silicone, I tend to use Platinum Cured as it tends to be skin safe with a sure hardness of around 20.
Push in the core and let it set.
printed a 0.2, 3 layers, in PLA.