[Formendacil]

Cirdan was still there.

As far as I know, there is NO evidence that Cirdan crossed over with Elrond, Galadriel, the Hobbits, etc.

On the other hand, there is a very clear statement (I can't lay hands on where it is, frustratingly enough), that Cirdan would remain in Middle-earth until the LAST ship departed.

It is quite clear that there were still many Elves in Middle-earth after Elrond's departure. Rivendell was still populated under the rule of Elladan and Elrohir, Celeborn remained with the remnants of Lorien. The Haven Elves themselves don't seem to have been thinned too much. Legolas and his Elves, and well as Thranduil's people remained. And as far as we can tell, although Gildor had left, there were still some Wandering Companies in Eriador.

Also, as Sam tells Elanor (and us) in the Epilogue (unpublished, but indicative of Tolkien's feelings on the subject), there would be Elves (even some Noldor at that) in Middle-earth for many long years to come. Indeed, I would say that there are STILL Elves in this middle-earth of ours, and that means that Cirdan is still here somewhere, probably at some small fishing town on the British coast.

It would appear plain to me that it was Cirdan who oversaw the building of Sam's boat. Perhaps there was a company of Elves ready to depart Middle-earth at that time anyway, and Sam arrived just in time to catch a ride, not unlike Bilbo and Frodo.