To your question where to send fish:
Dr. Edward J. Noga
NCSU College of Veterinary Medicine
4700 Hillsborough Street, Raleigh, NC 27606
In his book he has instructions what and how to send in and a form that should be filled out and send with the specimen.
In general small live specimen are preferred over dead ones.
Several fish with different stages of disease are preferred.
I hope someone here has a PDF of the form and can post it here together with the instructions.
Otherwise I would recommend getting a copy of the book - especially if you have so many fish.
As to your "outbreak"
Pictures and a detailed description would be helpful.
How are your tanks connected (rooms, order of flow, filter technology used)
Which fish are in which tank?
Which tank showed the first symptoms (not necessarily deaths)?
What kind of symptoms?
How did it progress?
Are there any tanks or fish that seem unaffected? Are there any that are especially affected?
What are your water parameters?
Have been any chemicals (cleaning agents such as ammonia, hairspray, deodorants, nail polish or nail polish remover, paints, smoking,... you get the idea) used near the tanks or even inside the room(s) where the tanks are located?
Who has access to the rooms with the tanks and what are they doing there?