Looking at what I now understand to be the missing bit, it shouldn't be too difficult to make one. You know the dimensions and it only needs to be steel in order to be affected by the coil. Perhaps a bit of old Meccano?
edited to say .... This is one of the best laughs I've had this week..... I have an image of 133 forum members having read this thread and all thinking "Well I understand.....????"