I saw that... unfortunately I haven't seen a marker like it anywhere. Have you checked Mike "Hawkeye" Picketts site?
I have heard of Spanish gold and silver washing up near Bandon and Coos bay, but no definate recoveries. Lynn Blumenstein did quite a bit of mag study, but it was mostly up north. I'd be interested in checking into your find a bit, more for curiousity than anything else. Send an e-mail with any particulars you care to share, and I'll check my books to see what may match up.