Hi William
The certificate for my boat (a 30 classic) was the last appendix in my owners manual. I presume there is not one in your manual but have you tried emailing all the 325 members in the association to ask them if they have a copy that they can send you. They don’t all sign up for notification of posts in this forum. You can get a list of owners by doing a search of the members list and then email them through the website.
Best of luck
Alan
The membership association for owners of Dufour Yachts