I have tried really long to get these clips replaced from Velux but they never answered. I lost them during the install (this happens, when you just moved, install several of these curtains and have a one year old kid playing next to you).
Finally I was able to build and print the replacement myself. And the kid is now four years old...
I used support but you can probably get along without it too.
The author hasn't provided the model origin yet.