Trim Enabler 3 is no longer sold separately, but it is included when you purchase Trim Enabler 4.
If you own a license
If you own a Trim Enabler 3, or a Trim Enabler 4 license, you can download all of the apps here: Download Trim Enabler.
Note: You may experience issues trying to activate older versions of Trim Enabler on older versions of macOS. If you are having errors about invalid input or missing internet connection, please see: Fix for "Connection failed: Invalid input or not internet connection"
If you don't own a license
Both Trim Enabler 2 and Trim Enabler 3 is now included when you purchase the new Trim Enabler 4. You will receive a download link and instructions for getting your license with your order email.