Scratch 3 is available for the Raspberry Pi: Scratch 3 Desktop for Raspberry Pi OS on Raspberry Pi - Raspberry Pi Foundation
You must be running Raspbian Buster to install Scratch 3. If you attended the July workshops at KSU, you have Buster on your workshop SD card. You can download the “vanilla” image here: Raspberry Pi OS – Raspberry Pi
If you like the KSU image, the version from the July workshops is available here: https://ccse.kennesaw.edu/outreach/raspberrypi/resources.php That one does not have Scratch 3 pre-installed, so follow the instructions in the first link to install Scratch 3.
Edit: Well, aarrgghh! I tried installing it from the terminal and got this error:
Repository ‘http//raspbian.raspberrypi.org/raspbian buster InRelease’ changed its ‘Suite’ value from ‘testing’ to ‘stable’ This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
The magic incantation to fix it is:
sudo apt-get update --allow-releaseinfo-change