150mm is far closer to what is needed for many really short riders and are not too hard to come by - try googling 150mm chainset. 165mm is simply too little difference. I have found over the years in coaching youth riders that about 0.21 of inner leg length (crotch to floor) makes for about the correct leg length. My experience has also been confirmed by others such as Chris Juden of the CTC in the UK. This results in the following:

Inner Crank
leg length
length
(cm) (mm)
71–72 150
73–74 155
75–76 160
77–78 165

Actual ideal length does vary a little depending on ratio of thigh/shin length, pedalling style, shoe size etc