might be that they are a break reward or carve, or that they are a reward from training missions, can't really say for the last one though
You are correct that they are a break reward.
Fatalis Eye can be obtain with about an 80% chance when you "break" the Fatalis face. Actually, you must break the face three times to get the Fatalis Eye.
As for Fatalis Webbing, you must "break" the wings. You will know that you've broken them when they appear scabbed near the top. I'm not sure if you have to break both wings or just one. Wouldn't hurt to do both though.