A couple Din helmets [pics below] have been auctioned by Julien's, but I don't think they're being used to offer anything to the community. The EFX and Anovos ones exist though so that's not a major concern.
I can't seem to find any darksabers ever coming up for sale/auction. The pics MF posted look good detail-wise, but he's always pretty cagy about this stuff and refuses to share the provenance, so it feels a little sketchy.
Where are all of these production props coming from? From people involved with the new Disney stuff that I've talked to, they're very strict about the props and everything is taken immediately to their storage/archives. It poses an interesting question I think then to who has these things to put out in the first place.