Sorry I ll have to pass on this one, at least for the time being.
It looks like the twin otter is more popular with Skydiving schools than scheduled airlines see
http://twinotterspotter.blogspot.com.au ... ory-e.html I ll give priority to models with larger user bases so more FG users are likely to see them at their local airport.
@Gooneybird has done the Saab models so you should be fine starting on a Loganair trafic file and maybe use these ones for the DHC flights.
Good luck with the project
Ian