... after a big mistake i took my longer screws to mount the rear wheels and tryed to drive.

I stoped immediately after i noticed a scratchy sound from the right rear wheel.

Changing the screws to the normal shorter one was easy, but a scratchy noise was still present.

Then i started to dismount the rear brake and took the disc off the axle ... i found a lost deformed spring behind the disc.
My questions are:
Where was that spring? How to get i back mounted and if it is not possible to repair that spring, is it possible to get only a new one?
Hope some of you guys can help me with that prob, cause i cant drive to the next dealer to get it fixed.
Here i added some pictures of that spring and the dismounted disc/handbrake:
