First, from your Project List, click to add your 'Custom Columns' (Learn More)
Next, add in your 'Sales Office' column.

Now you will be able to see your projects by Sales Office.

You can also Filter your Project List by Sales Office. Don't forget to include archived projects if you're looking for events that have already been completed!

Pro-Tip: Export your project list to excel for in-depth reporting. (Learn More)