As far as I’m aware most Dovo shavettes come standard with the red insert. However, in case yours came with a black or green insert or you simply lost the red insert then the best place to look is online.
Most places that sell the shavette will also sell the inserts for you to purchase separately. Typically it will cost you $2-$3. Here are a few places where you can buy a red insert:
This is one of those cases where you are probably going to end up paying as much in shipping costs as you are for the price of the insert itself. If you don’t need it immediately I would hold off ordering it until you have something else to purchase and then purchase everything at once.
As usual let me know if you have any questions. 🙂