Thats a lot of interesting travelling! I know Scandinavia quite well, but haven’t got a clue where half those IATA codes are!

Well, at least a few lesser known codes i can tell you…

TRD Trondheim
RVK Roervik
BOO Bodo
ANX Andenes
KKN Kirkenes
VDS Vadso

RE: Sheffield Airport.

We have similar problems here in germany as well!
I live near Mannheim City Airport (MHG) some 50mi south of Frankfurt that has also a short runway (TORA 1120m). The basic problem is that most airlines are not willing to invest on a new destination these days even when everybody knows there is a substantial market. It´s crazy. We have a single operator here (Cirrus Airlines) flying to Berlin-THF and Hamburg with average loadfactors around 75%!!! And they´re making a lot of money as 85% are business-travellers that are paying full fare…
Mannheim has the highest frequency to Berlin of all german regional airports (up to 5 flights a day – mo-fr) They are not willing to operate Dash 7 on that route as it is considered as too expensive to operate although the morning and evening flights would even then soon be sold out! So they continue to fly with Dornier 328 and partly Dash 8-100