Why not let everyone who unearthed a particular detail about a costume or prop decide for himself if he feels like sharing it with the community?
People in general seem to just assume recently it is a duty to not keep certain aspects to oneself. Mostly even without contributing something to the community themselves: it's easy to demand things from others if you are not the one who has anything to share.
Show your gratitude to those who share and just leave the ones who don't share alone, it's that simple, to me at least.
Showing up as a mob with torches on a "hoarder's" porch won't change his mind to share, will it? Maybe asking quietly and in a non-demanding way is a better way to approach someone who knows/has something you might want...
That's my 2cts, I sure as heck don't mean to offend any one person in particular, I'm only trying to illustrate my point so everybody gets it.