The label that displays in the Available Ticket Classes table under the Qty column can be customized via the Message Catalog Editor.
  1. Navigate to Setup > Product Configuration
  2. Select the Message Catalog Editor tab
  3. On the left hand side of the screen, select Tickets under the Application drop down menu
  4. Click the Refresh List >> button
  5. In the search field, enter N/A
  6. Click Search
  7. Under the Actions column click Edit Custom
  8. In the Enter Custom Text below: text box, enter the desired text (Sold Out)
  9. Click Submit