The Númenoreans had really big ships.
Quote:
...a vision came to [Aldarion] of a mighty vessel like a castle with tall masts and great sails like clouds, bearing men and stores enough for a town.
(UT II 2)
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And since the Númenorean exiles were concentrated in cities/towns - e.g. Fornost, Annúminas, Osgiliath, etc. -, the nine ships would have sufficed.
Aside from Pelargir, there are also Númenoreans in what would become Arnor.
Quote:
...thence many [of the Faithful] set sail to Middle-earth seeking the northern coasts where they might speak still with the Eldar in the kingdom of Gil-galad. This was known to the kings, but they hindered it not, so long as the Elendili departed from their lands as and did not return...
(Akallabêth)
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So not only Gondor had pre-Fall Númenorean populations, but Arnor also. Alas, they arrived later, so they had less time to multiply before the War of the Last Alliance.