Regular plugin releases are available from plugin repository.
You can setup auto-update of Scala plugin Nightly builds in IntelliJ IDEA in the Preferences menu under Preferences | Languages & Frameworks | Scala | Updates
Select the Nightly Builds update channel from the drop-down menu:
If this does not work, add "https://plugins.jetbrains.com/plugins/nightly/1347" to custom repositories under
Preferences | Plugins -> Gear icon -> Manage Plugin repositories:
Nightly builds are no longer published to confluence. Check the Scala Plugin page on the JetBrains Marketplace for updates and downloads.