I've also not seen one like it. BSA could easily have done something like it themselves and I think it was a case of thinking 'if it ain't broke, don't fix it', sales-wise, that they didn't. Plus perhaps a bit of pre-WW2 imperial arrogance?
I've always thought it a shame BSA didn't take a leaf out of Diana's book and copy their half-stocked underlever rifles of the 1930s - which in turn were updated ripped off BSA designs.