Just got back to designing new locos. One I had been planning was the 50cm gauge Crochat locos as found on CF de Tarn. Such ungainly machines. Design is for 1/32 to go on 16.5mm gauge track, but given the size of the cab, and its narrowness, I think it could easily be used for Gn15.
It is a big model(19.206cm / 3.55cm / 7.598cm), so price will be about £65, based on today's Shapeway update(suppose it might depend on exchange rate as well)
I have deliberately left the cab empty to make it easier. Also I could not see details in photos.
The unusual motor bogies are difficult to model, but for me a simple Lima bobo loco will do, A dummy wheel can be added between the 2 on the chassis.
I have already looked at the design in smaller scales(1/76 and 1/87), both of which should fit on Z gauge chassis I think. Version in 5.5mm/ft to fit on 9mm gauge, so this might suit O9 as well. This would be about £21.By shaving off a bit of plastic in the design, price could be brought down a bit.