Rear Light for a Harris Framed TT2 Replica

[ducati427]

I have a harris framed TT2 replica (pantah) from the mid eighties and need to find the correct rear light lens as mine is cracked. It must be a common part, probably off a jap bike from the early eighties . It is marked as a Stanley 040-6626 Japan AU400. Other markings include: D8M 35797, LPXARLT, A (in a circle)39942, E4 (in a circle), 60R-0081 and BS2516 GRADE-1 It is a rectangular fitting. Once I know what it was originally fitted too I'm sure that I can find one so any inspired ideas would be much appreciated. thanks Paul