In the recent release that had recipes for runes and sigils, we did not receive a sheet or making Karka Slaying sigils. They have been long out of circulation and I'm sure there are a few players that would actually use these items, so the recipe sheet is conspicuous by its absence. Strangely, karka drop a recipe sheet for Grawl Slaying sigils. I have a theory that the wrong item was assigned. One of the neighboring item IDs in the API is unrevealed, and could easily be hiding the proper recipe sheet.