the Raspberry Pi 2 img retropie-v3.5-rpi2.img
but before using in your Pi3, you’ll need to…
sudo apt-get update; sudo apt-get dist-upgrade
it’ll fail at the bluetooth set up, but thats fine, safely shut the pi down,
insert the sd card into your Pi 3, allow it to fully boot, exit emulationstation,
and finish off, with
sudo apt-get update; sudo apt-get dist-upgrade
then reboot