Hi H_581,
I am Dave, I will help you with this.
Microsoft stopped selling Windows 10 on 31 January, they only sell Windows 11 now, usually after a new version of Windows is released they stop selling the previous version a year later.
The only way now would be to get Windows 10 from a 3rd party retailer online, or from a PC shop that may have a copy of Windows 10 left.