The Scan.conf file is found in:

Windows 7:

C:\Program Files (x86)\Toon Boom Animation\Toon Boom Harmony 10.0\etc

Mac OS X:

1. Application > Toon Boom Harmony 10 > tba > etc
2. Hold down [CTRL], click Shared Modules and then select Show Packages Contents.
3. Open the etc folder.

Linux:

/usr/local/ToonBoomAnimation/harmony_10.0/etc