I have been real busy as of late. I think I have a very good lead that might help us find a part that has never been officially ''found''.
My source had a discussion with Jeremy Bulloch a few years ago and while talking to him he has found out that the missile part was constantly breaking and was fragile. It seems that part was actually not custom machined but really, like many other costumes or decors in Star Wars, a model kit part. While I cannot say exactly from which model kit it came from, I have a good reason to believe that it came from a Helicopter Model Kit. In fact, I can even venture farther and say that it was a missile pod from a russian MI-24 HIND helicopter. I have not calculated the scale but it might also be from a RC helicopter...
Here are a few pics for comparison :
The real deal russian MI-24 HIND helicopter :
From a RC helicopter :
I believe that it would be possible to find the real part with some help from the community. I also understand that the part might have been altered so that might be a small bump in the road.