AliExpress full of replacement remotes, costs under 10$

Airmouse USB remote from Amazon they are nice

Buy another remote or mi box.

Or buy a usb/Bluetooth keyboard

This new WeChip G40S remote is the best going around for a Wireless Voice remote replacement:

https://forum.kodi.tv/showthread.php?tid=252916&pid=2989937#pid2989937

I don't think you can set them up without the remote...