Can't help you on the motherboard issue, but I sympathise with your view of Sony 'support'. They will not provide spare parts (of the component variety) to anyone, even vendors - hence the reason why you are having trouble finding one.
You should also be aware that even though the models here and in the US look similar they are different models, have different BIOS'es etc.
You could try this forum
http://sony.thumbrocket.com/ they have helped me in the past.
Good luck!