Handle such inquiries in character.
Posting rare CNR item properties on the forums has been officially frowned upon before, however it isn't a rule and not something anyone on the team has time to enforce anyway so its one of those things that would be great if the community would shy away from.
reasoning:
Finding this stuff out if part of the fun. Especially a new/newish recipe. Back in the day a good portion of rare recipes had never been made before and finding out if anyone had made one, searching down who had seen one, or getting everything together to make one or have one made yourself was a bit of an adventure. Lets preserve that fun for the new players who weren't around in the period when everything was new. Keep the feeling of newness and discovery alive for them too.