Does anybody know where can I buy a power cable for this router? Or
even a good substitute for it. How do I find one?

https://www.tp-link.com/uk/products/details/cat-9_TL-WR841N.html#overview

The power cable of my router is damaged and so the connection is dodgy
or does not connect at all. The router is quite good because I have
tried using a cable from other router.

Thank you.