Anxiety Measures
In general, outcome measures have been developed to measure symptomatology, as opposed to specific anxiety disorders per se, since no brief paper-and-pencil measure is sufficient to actually diagnose any disorder. Also, you would need to be careful to determine whether the measure has been validated for repeated, weekly use. In some ways, it would be easier to use one of the general symptom checklists (i.e., SCL-90, Hopkins Symptom Checklist) for all the patients.
Given those cautions, there are many anxiety measures out there. Unfortunately, I do not think you can legitimately avoid going to the trouble of checking out the research on each one to determine which would be valid and reliabe for your purposes. I will just list a few of the options here to help you get started:
For anxiety symptoms in general: Zung Anxiety Scale, Beck Anxiety Inventory, Hamilton Anxiety Scale, Taylor Manifest Anxiety Scale, State-Trait Anxiety Inventory
For Panic Disorder: Body Sensations Questionnaire, Mobillity Inventory, Agoraphobia Cognitions Questionnaire
For Phobias: Wolpe-Lang Fear Survey Schedule, Marks and Mathews Fear Questionnaire
For Social Phobia: Liebowitz Social Phobia Scale, Fear of Negative Evaluation Scale, Social Avoidance and Distress Scale
Obsessive Compulsive Disorder: Maudsley Obsessional Compulsive Inventory, Yale-Brown Obsessive-Compuslive Scale, Compulsive Activity Checklist
Good luck!