Hi Alexander,
You could try John Gillard at Classic Citroen Restorations in Kent. He has a lot of spares.
Email: citroenclassicrestorations@btconnect.com
You are looking for a Perfo head.
BTW – this post is actually in the 6-cylinder section of the forum. You might want to re-post in the 4 cylinder part.
Chris
Chris