The half moon part is crucial to forward pressure. Without it your binding will not pass an ASTM (American Standards for Testing and Measurement) test. Keep in mind that these bindings were originally designed for racers, that do not put a lot of impact on the binding like park and freeride skiers. Along these lines, most racers use the bindings for a season and then move to a new system the next year. Also Race Stock is designed to be thrown away if it breaks, so there is not a very big market for replacement parts.
As somebody said above, if your local shop is a big LOOK/Rossi dealer and the tech has skills with this system, you may be able to get parts and get them fixed, however it is not as easy as sending a broken ski back to be replaced on warranty.
Skis have gone through a lot of changes because of the abuse we throw at our sticks. Bindings are next in the tech boom.....I hope...
Also note, Quicksilver actually stopped production of these a few years ago feeling there was no need for the system. After a loud response from the racing and freeskiing communities, they brought the system back, however there have been no significant upgrades or design updates to the product.
Hope this helps
