There are 2 different Asus FX505DD displays available and each display also has equivalent substitutes.
Here's a link to a supplier that may help to find a replacement.
Search online using the Asus part number only for the display (as shown for each display) to find suppliers and prices that suit you best e.g. 18010-15670400.
Note: The unavailable designation applies only to the supplier linked and not that it is not available anywhere else.
If you wish to confirm that you're ordering the same display, usually the part number can be found somewhere on the back of the panel itself.
Here's a video that shows how to replace the screen in your model laptop that may also help..