Hi @webworks welcome to the /e/ forum.
The list of devices supported by Easy Installer is here Try the Easy Installer beta. Your phone is not supported.
Looking in Smartphone Selector the phone Info about Samsung Galaxy S III (International) - i9300 is marked “Legacy”, that is to say
Warning: Devices marked as legacy will no longer receive any updates from the /e/OS team. In the future, some devices may still get updates with support from the community.
The install instructions are found Install /e/OS on a Samsung Galaxy S III (International) - “i9300”.
Last month /e/ experienced a server outage a side effect of which is that “older builds” are not found on the servers. When the ROM is available again this will be the link https://images.ecloud.global/dev/i9300/ but it shows “Not Found” at time of writing.
Searching UnOfficial Builds finds [UNOFFICIAL BUILD] Samsung Galaxy S III I9300, I9305 for /e/OS-Pie