Hi,
As it is a recently released model there probably aren’t too many parts suppliers who have the parts yet.
I found one [https://www.fixo.com.au/collections/google-pixel-5a-parts|supplier] but that was all.
You may have to contact a supplier that has Google Pixel 5 LCD screens and ask if they can get screens for a 5a model from their suppliers.
Here’s the Ifixit [guide|140507] guide to show you what’s involved when replacing the screen. Your model may differ slightly in what has to be done but hopefully not that much