What is a good substitute for puffin? I am trying to recreate a faroese dish of braised puffin stuffed with cake.

As I live in the UK, puffin is not a meat that is easily available (if at all).

To anyone who has tried puffin or knows anything about the meat's characteristics, what would you suggest as a reasonable substitute?

My first thought would be a wild duck such as teal or mallard, but these tend to be very lean meats and would not normally suit the 90 minute cooking time suggested in the puffin recipe, which makes me think puffin meat may be quite different to how I imagine it.
I have had smoked puffin once in Iceland. It made me think of a lean, strongly-gamey/livery duck/goose breast that's been sous-vided till very tender - I remembered the grains (meat fibres) to be very fine. There was a mild sort of silky fishiness (that was masked by the smoked preparation) too, but I'm not sure if I imagined that knowing the puffin was a seabird. 

I googled faroese puffin (here), and I think the 90min cooking time is meant to ensure that the batter sewn up in the bird is properly cooked -> making the puffin merely a slow-cooking vessel for the cake within. 

If I had to hazard a guess, and you could forgo the aesthetic of a whole stuffed bird, then perhaps you could mimic the flavor by sousviding goose/duck breast that had been sewn up with the batter, with a bit of liver in the bag (unless your duck was already very gamey). I'm not sure how (or why) you would add that element of fishiness.