Know idea what notebook you have but the older G75 G55 G46 have the button next to power button that only changes Power schemes, I don't know anyway of programing it to act as a power button. Its sounds like your having some serious Over heating issues. you will need to solve before you worry about replacing the power button. EBay is the only source of part I know of here in the states the EU I believe there is a parts dealer in UK you can goggle that one up. The kind of heat it would take to screw up your power button would indicate a charger problem on your Mother Board? Sounds like its about time for a upgrade to me?
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro