The usual disclaimers apply: it’s not mine, I have no affiliation with the seller, and this is just being posted as it may be of interest to C&F’s membership.
On a whim, I searched for low D whistles on eBay. One such listing was a brass Copeland low D. The pictures show a whistle that appears to have some minor and honest wear. As of this post, one bidder is willing to part with at least $750, plus shipping and tax, to own it.