Considering that IISExpress is 32bit, you should use the 32bit version of NCryptoki dlls and you should load the 32bit version of the Luna Cryptoki dll.
The problem you got is that you are using the 64bit versions of Luna Cryptoki instead (the path is C:\\Program Files\\LunaSA\\cryptoki.dll and Program Files on a 64bit OS contains all 64bit programs while Program Files (x86) contains all 32bit programs).
You cannot load in a 32bit process (IISExpress) a 64bit dll (Luna cryptoki.dll).
Regarding the GAC, it's not strictly necessary the GAC registration. You can simply copy NCryptoki.dll and NCryptokiMngd.dll in the working directory of your app or in the bin folder of your webapp or in system32
Regards,
Ugo Chirico