why are you so sure labrador rescue won't find CoCo and Cookie a home together?
it usually is harder to place a pair of dogs than one dog (who may go to a home where they already have one or more dogs) but it's not impossible.

also have you looked for dog lovers' sites to post similar messages on, including any that specialise in retrievers (you could join a labrador and/or all-retriever/gun dog yahoo group for instance)

if doing a private adoption be careful who you rehome to and do ask for some donation (which could go to an animal rescue group perhaps)
If you are going overseas it would be good to have a rescue group to be a backup to take the dogs if the adoption doesn't work out for any reason