Natural Revelation is there so that everyone will be accountable for the truth, and if they ignore it and turn away from it, saying in their hearts, that's it's not important, then they are eternally condemned. But, if anyone, even a non-elect person, sees the Natural Revelation and responds to it by seeking to know "who" it is that is "out there," then God is obligated to bring to them the "Special  Revelation," which will always be about Christ.

I find support from this from 1 Chronicles 28:9 "...If you seek Him [God], He will be found by you; but if you forsake Him, He will reject you forever." God will reject anyone who "forsakes Him" -- that is, those who reject His truth, be it Natural or Special Revelation.  So, a non-elect person can never say, "I responded to your Natural Revelation, but you never gave me the Special Revelation, therefore I could not believe."  God, is simply being faithful to "anyone" who seeks the truth that He will, "by the Holy Spirit" give them the truth, but they must love the truth and accept it.

In the case of the "non-elect seeker"--one who responds to Natural Revelation, but then rejects the Special Revelation he receives, then God says of them, "They perish because they refused to love the truth and so be saved" [2 Thessalonians 2:10].

I think we should also remember, that simply hearing the message about Christ will not save anyone, for Judas heard it for three years--no, what saves someone is the "free gift of faith" [Ephesians 2:8-9,  the ability and desire to repent, believe, and submit], and this free gift of faith comes through hearing the message about Christ [Romans 10:17], but only to those who have been chosen (elected) before the universe was created.

Thanks for asking the question for it has caused me to put some more pieces together, that the Holy Spirit does draw people to Christ, but only the elect will love the truth and so be saved.  It is not that the non-elect "can't believe," but rather that they "won't believe, because they don't want too."  God is allowing the non-elect person to make a freewill decision to either accept or reject Christ.