Gazillions of them online...plastic, carbon etc.
However, be warned, they can foul the tyre at the sides of the extender, the extra weight of the extender can make the whole mudguard flex and this can have two consequences.
First and merely irritating, is a constant chirruping from the front end as the extender contacts the tyre.
Second and more worrying is that the front mudguard can crack up in the acute angle at the top of the guard. This can happen even without the extender mind.
Good that the dealer cleaned the rad. I hope you check to make sure it was done thoroughly...