Some targets use webforms. Some use email addresses. Some maintain both. Is there a listing of all targets, with their webforms and email addresses, and an indication of what they use?
There is no public list available for this. Whether email or webform is used, for a target, can change depending on the availability of the webform (they can go down and it's outside of our control). So any sort of list we attempt to provide for this might be moot from day to day (or month to month) as updates from our data provider come in.
If you prefer to direct your advocacy message to a specific staffer, for example, you can absolutely use a custom target for that purpose. That may open up the door to action-takers from outside the intended district, but you could target (email blast) your supporters using a district-targeting query (in the Target tab of an email blast) to minimize that.