One of our partners may have a outdoor antenna solution for you, their website : https://poynting.tech/
It may also be worth considering using external outdoor casing for the router, and then use the antennas that were included in the device. However consider the size of the casing, to know whether you will be able to screw the antennas on afterwards.
We currently do not have outdoor antenna or casing for RUTX14. As mentioned, you are always welcome to try a third party solution, we cant advise much on that, as our devices have not been tested with them.