I have a modest but hopefully useful idea.  Perhaps someone who is
web-savy could take a map of the United States as a web site with
hyperlinked dots marking the locations of known good ferret vets and/or
shelters.  Another option would be a web site with a State by state
listing of shelters and vets.  I will contribute a reference:
 
Brandt, Paul DVM - Westgate Pet & Bird Hospital
(512) 892-4463 4534 W Gate Blvd # 103
Austin Texas
 
I have had all 5 of my ferrets treated and 3 operated on there with
outstanding success
[Posted in FML issue 4186]