Other than shelters & pet stores which offer pet sitting services, or
having a friend watch them, I don't know of any other options.  Some
vacations can include travelling with your ferrets...it involves a lot
of preparation, getting hotel/airline arrangements, etc., and even then
sometimes it isn't possible (such as if you're going to Hawaii).
 
If you had posted your name and location, perhaps someone on this list
could have agreed to take them in for 3 weeks.  I've seen that happen.
I'm in Chicago, let me know if I can help.
 
Good luck.
 
Chana Rosen
[Posted in FML issue 3584]