Coffin cover is unobtainium. I’d like one too. PPS was looking into it a few years ago, but I don’t think anything came of it. Also a few years ago, somebody 3D printed a cover, but it didn’t look anything like the original.
https://pinside.com/pinball/forum/topic/what-parts-are-unobtainium/page/5#post-3305303
(posts 208-211)