To add a quick availability to check to you account firstly enable the setting on your account to do this.
Click into [Settings] link from the left main menu
Then click on [Boarding] link from the side menu
And set the [Add Availability Step to Booking Wizard] to 'Yes'.
Once enabled when you go to the [Add Booking] wizard once you enter the requested dates you will see a new step showing you run availability for the dates in question.
You can further expand this screen by also selecting the 'Shows Run Names when showing availability' - this will expand each section to list the individual runs that are free for the booking duration.