This is an odd question since it seems to imply that those in the Church have yet to be saved. It's the phrase "only possible for those in the Church" that prompts me to think this. Scripture tells me that the Church is made up of born-again people, those who have been saved, not those who may be saved. Salvation, then, isn't merely a possibility for those in the Church but the means of their membership in it.
If what you are asking is actually, "Can people be saved apart from hearing the Gospel and trusting in Christ as their Saviour?" I would refer you to Scripture:
John 14:6
6 Jesus said to him, "I am the way, and the truth, and the life; no one comes to the Father but through Me.
Acts 4:12
12 "And there is salvation in no one else; for there is no other name under heaven that has been given among men by which we must be saved."
Romans 10:13-14
13 for "Whoever will call on the name of the Lord will be saved."
14 How then will they call on Him in whom they have not believed? How will they believe in Him whom they have not heard? And how will they hear without a preacher?
Romans 1:16
16 For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.