[The Squatter of Amon Rûdh]

Well, there are roughly 103 years of which we have no account. The three were made in S.A. c.1590; Celebrimbor discovered Sauron's plot in S.A. c.1600, and the Three were hidden in S.A. 1693, so I can see how this question arises. Legolas and Joy have given you the best answer that the books can supply, though. I can't claim to have made an exhaustive study, but I'm fairly sure that never in any of the writings available to us does Tolkien mention by name any keepers of the Three before Gil-galad, Círdan and Galadriel. This includes the published letters, the early drafts of LotR and all post-LotR versions of the Silmarillion. What Tolkien does say, however, is that:

Throughout the Third Age the guardianship of the Three Rings was known only to those who possessed them. But in the end it became known that they had been held at first by the three greatest of the Eldar: Gil-galad, Galdriel and Círdan.

[The Return of the King, Appendix B, p.365 (first edition). My italics]

As for the discovery of the plot, the Tale of Years has this to say:

c.1600 Sauron forges the One Ring in Orodruin. He completes the Barad-dûr. Celebrimbor perceives the designs of Sauron.

[Ibid, p.364. My italics]

Those are the facts as matters stand. My guess is that Tolkien means what he says and that the Three were given first to the named parties. Note that no mention is made of when this first giving took place: it could easily have been when the Rings were hidden, which would only mean that Celebrimbor held the Three in his charge for just over a century. Nor is there any particular reason why at first the rings should have been given to different people rather than being stored in a treasury: they were separated in order to make it more difficult for Sauron to acquire them. Since Celebrimbor was the ruler of Eregion, the smiths thereof being subject to him as such, it does not seem altogether unlikely that he should have been the Rings' original keeper. This would explain why in the Tale of Years it is he who is specifically mentioned as the uncoverer of the plot. Also it seems unlikely that he would entrust the Three to anyone but the named keepers once Sauron's plan became known to him, so the questionable period is only ten years: a short enough time for an Elf. If there were any anonymous early keepers then there is no record of them. In history, that is as close as one can get to being nobody.