Since moving I haven’t touched mine as there has been far too many jobs to do, so it’s has been far too long!! That said I just put a consumer unit in so I now have power and lights and every intention to start up again.
But the answer to your question is I think I’m gonna have to get one made, I have bought 3 different types of exhausts and none seem to fit, one was close but was still no good.
I’ve decided mine is going to be a side exit as well, seen as it’s going to be a custom job!