Elves and Gondor

[Inziladun]

Originally Posted by The Mouth of Sauron

As they were leaving Lorien Celeborn spoke to the Company - and it was obvious he was well informed about events in Middle-Earth. For example, he knew about the bridges at Osgiliath being down and the eastern bank of Anduin being held by the Enemy. He must have got his info somehow..

Celeborn probably knew about that long before the Company arrived at Lórien. Boromir had told the Council of Elrond about it, having witnessed it himself.

Originally Posted by The Mouth of Sauron

And as the Company was approaching Rauros Aragorn did state that boats in recent times had travelled down Anduin from Wilderland to Osgiliath - Boromir confirmed this, although he said it had happened "seldom". Might these boats have carried Elves from Lorien and also possibly from the Woodland Realm in Mirkwood ? Anborn knew about black squirrels in Mirkwood..

Aragorn could have travelled the River by boat on many occasions during his journeys. The same goes for Boromir, though I'm not sure what reason he might have had for being in a boat approaching Rauros from the north prior to the Company of the Ring.
That was also the probable means of Lórien elves to rendezvous with any men of Gondor they would speak with, but I know of no evidence Thranduil's elves from Mirkwood ever did the same. Anborn's words about the black squirrels were probably just from folklore he had heard.

Originally Posted by The Mouth of Sauron

Another possibility I suppose would be Gondorian ships sometimes going to the Gulf of Lune, and/or Cirdan's mariners visiting Pelargir.

I wouldn't think either would have been likely, at least not for many years prior to the War of the Ring.
The last instance of ships from Gondor going to Mithlond that I know of was in the year 1975 of the Third Age, when Eärnur brought the army that defeated the Witch-king. I think Gondor became entirely engrossed in their own affairs after that, and would have seen no profit in such a journey.
Círdan, too, would have had no call that I know of that would bring his ships to Pelargir. He and his people were pretty well confined to Mithlond and Lindon by that point. I get the impression Galdor's trip to Rivendell was a rare event.