Yeah, I guess I should just call. I asked them about it a couple of months ago and they said they didn't have any spares at the moment, but were expecting the next shipment in a few weeks. I figured it had been long enough to check again...
I'm not saying anything was wrong with the kit; it was all my screw-up. It it comes down to it, I saved the wood from the rib sheets, so I could trace them and cut out new ones. It would just be easier to have the new set, though.