Here is my old thread, maybe you will find some inspiration there 
I have been to a lot small airfields (small for an airliner of course) since I have bought the 737-600, maybe I will add some more to my thread, even though it is closed. Anyway, you can also try Sumburgh (EGPB) which has 2 short runways, El Hierro (Canaries, GCHI), Kamembe (HRZA) in Rwanda is also quite challenging (short runway + high altitude), Guernsey (EGJB), Isafjordour (BIIS) is awesome, TDPD on Dominica is also a challenge (RWY 09) and Carib Express used to fly their BAE146s there