Necessity is the mother of invention
Cher Sylvain,
It is said that necessity is the mother of invention. I submit to you the following examples of necessity leading to invention, and improvisation.
These owners met the challenge typically using rubber bands, zip ties, or clamps to secure the front fender stays to the Sofrider's "fork."
If this kind of improvisation is beyond your ability, take these pictures to a local bike shop like,
www.mec.ca, who are resourceful, helpful, and will offer you a solution.
As I mentioned previously, the best fender, in my opinion, for the Sofrider is the SKS Longboard because it offers the greatest protection/coverage.
Bon chance, mon ami.