Otaku-sempai wrote: Question, were the Elves of Lindon and the Grey Havens in the Third Age exclusively (or almost exclusively) Sindar? Or might some remnant of Gil-galad's followers (presumably Noldor) remain?
That's not easy to answer. Off the top of my head I remember a note in UT that the Elves of Harlindon (=the part south of the Lune) were largely of Sindarin origin. Nothing else is said about the rest, but this stressing of a dominating Sindarin population in Harlindon might imply a more Noldor-dominated elvish population in Forlindon.
Whatever the case, the most important feature of the elvish population of Lindon in the Third Age is its constant dwindling and therefore a steady negative population dynamic. Over the course of the Third Age more and more Elves of Lindon leave Middle-earth for Eressëa.
So in an early or mid-TA setting, you are certain to have a much higher total number (and proportion of Noldor) of Elves in Lindon than in the TOR era. In the latter timeframe, it is conceivable that only the Mithlond area still contains a noteworthy population, with all other settlements abandoned already. Compare this to the end of the second millenium TA, when there were still at least two sizeable harbours more in operation as Gondor's expeditionary forces landed in Lindon to aid Arthedain against Angmar.
EDIT: Pengolodh, the elvish loremaster whom Tolkien used in many of the texts in the later HoME (and who supposedly compiled the many of lore available to us) is said to have lingered long in Middle-earth, but at the final arising of Sauron in TA 2951 he finally gave in to his fears and departed for the Undying Lands. This is a convenient date to place the last big exodus wave of Elves from Lindon who finally departed and left Círdan with only a small population remnant for the next seven decades until the war of the Ring.
Cheers
Tolwen