I’ve got a spare Surly stainless 104 36t chainring if that’s any good. It’s designed for 1x or single speed so it might not be for you as there’s no ramps. I found it fine as part of a 2x with a 22t inner.
Thanks - I might take you up on that. I'm waiting to hear from my LBS, who are trying to persuade me they can fettle a Shimano middle ring, though I'm a bit sceptical as I think it will mess up the spacing.