Finding replacement KeyCaps and the scissor mechanism for the Magic Keyboard systems is still hard both due to the newness and COVID messing up the supply chain.
As much as I hate sending people to Apple I think that’s really your only hope. If you took out AppleCare+ coverage then you’re golden!
Here’s the only source I know of [https://www.thebookyard.com/apple-keycaps-clip-select.php?cPath=66_510_499_725|MacBook Pro Late 2019 - 2020 KeyCaps] Click on the picture to dig deeper. The arrow keys have been on short supply.