Unfortunately it is a bit of a trek for me ( around 300 miles ) so I am being incredibly lazy and sitting next to the wood burning stove with some nice flannel pyjamas on tapping away my J2 'wants'.....
The later J2s, i.e. from J3529 when the electric wiper was introduced, used the rectangular Lucas 160 mirror mounted on the off side screen support. Not a bad compromise if you don't find what you're looking for.
The earlier cars just had the useless central mirror mounted on the horn button. 'Useless' because it vibrates so much! It was done away with when they changed to the side mounted one at J3529.
There is a Lucas 1160 mirror on ebay at the moment Item No 272458782142 selling for £105. I suspect the price is about right. The arms are available new from usual suspects.. Rich