I see these model was introduced in February 2015, so it's 4.5 year old now. I assume it's out of warranty by now.
Motherboards are very laptop-specific. If Toshiba doesn't sell them anymore, look at eBay for a second hand laptop of the same model that you can use the motherboard of. Or, much easier, use the whole laptop in stead of your current one. Or, still easier, buy a other, newer, model.
I can't find a motherboard for my Qosmio X70-B Laptop that came with an inherent fault with the logic board.
Please help me find one that can support my CPU
Intel I7 4710HQ
Socket: 1364 BGA
DDR3 RAM 8GB