-Dump in a local river?
-Sneak into a predator-protected pond at the arboretum?
-Take to a local stone yard, where they have ponds, and someone said she took her fish there one year... But this place frequently has EMPTY ponds, so if they have leaks, I don't want to bring my fish there.
PLEASE Do NOT do any of those options.
Domestic fish should never be released into the wild, they may outcompete native fish for food or transmit diseases to wild fish.
Post them on Craigs List or on eBay for local pick up only
Call other fish or pet stores and see if they will take them, I take mine to a store for credit
Contact local watergardening/koi club and see if they know anyone who might need them
Post on other pond forums to see if anyone in your area might want them. Like Garden Web, post on the section for gardening exchanges in your area too.