In the announcement "Lockboxes, Accessories and More!" from October 5, 2011 it is written:
Bugfixes

- Costume items may be sold for 1 crown to dispose of them.

... but this does not seem to work with the Authentic Dark Harvest Festival Masks.
I have some of them twice, they don't have accessory slots, they come pre-bound and they can't be unbound (because they are costumes and there is no 0-star unbind ticket). So they can't be sold in Auction House, can't be traded and can't be sent by mail, because they are bound. ... and I can't even sell them to Bazar vendors.

I understand that it is not a critical problem, because they don't do much harm except taking up space in the Arsenal, but ideally i would like to sell or trade them to get something useful for it, even if it's just one crown (like the announcement said).