Henin-Lietard is now called Henin-Beaumont and here is the address where to send your request:
Place Jean Jaures
62110 Henin Beaumont
If you read French, go tohttps://www.acte-etat-civil.fr/DemandeActe/PostValidationCho...
where after accepting their conditions, you fill up a form to request your document, print the form, and mail it to the above-address.
If you need help, contact me directly and I’ll be glad to do it for you. I believe the “Mairie” does not charge anything; at least from my experience with other Mairies (Courthouses).