This part rarely if ever fails. It would help to know how/why you think that this board is the problem. If you are looking for a replacement, I would suggest that you locate a defective Xbox One on the cheap and salvage it from there. Most failures of these machines are either the DVD or the motherboard (due to overheating). Thatbeing said, there is a good chance that a dead unit will have this board working as expected.
If you just can’t turn on the system, I would suspect that the tact switch (power switch) has failed and you should be able to locate a generic switch that will replace the one on the board. I would start there are switches are usually less than $1.
Update this with the original problem and we may have other suggestions.
Dan