I need to access the handle of the window for a dll ...

Hello, Been some time sense I have been on here last... Anyway, I have a way to play MIDI files on unity... I use a .dll... This dll requires a window handle though... How do I access the editor window handle or the executable handle? or if need be, create a new window form? I know I need to use using system.windows.forms but unity throws an error. also The dllimport thing looks kinda like this.

 [Dllimport("midi.dll",CallingConvention= Callingconvention.cdecl)
 public static extern double midi_init_ext(Double windowHandle, Double Device);

This is a very easy approach in C# alone but It is causing me a problem in unity... Thanks to all in advance