WTB - Fritschi Freeride Pro heel part

I installed a pair of the red Freeride Pros on my friend's kid's skis. I didn't have those red plastic plates that go underneath the heel riser/lock (which you can see in the picture I linked). It appears that, without them, the binding can pop out of the locked position -- not very easily, but it's happened 1/2 dozen times. I didn't know that those things were useful (and maybe it's something else -- he thought it might have been my (superb) mount job, so he even had a shop remount them with a jig. Problem continues.)

Anyone have some broken Freeride Pros and willing to sell me just the plastic under-heel plates (or know how to solve this issue -- wrong thread for that question, I know, but I'm a perma-jong)?

Thanks!