What is God's perfect will...Where can it be found in the Bible?
Romans 12:2 tells us to be transformed by the renewing of our minds, that we may prove (examine, test the validity of) "what is that good, and acceptable, and complete, will of God." In order to do that, we would need to know what is the complete (perfect) will of God, so yours is a very good question.
You ask, "Where is it found in the Bible?" The simple answer would be to change the punctuation in your question, "Where is it found? In the Bible." Let me explain.
I believe that the Bible is the complete word of God. "According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue: Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust." (2 Peter 1:3-4) We have all things pertaining to life and godliness through the knowledge of Jesus which we get through the Bible.
In Ephesians 4:11-16 Paul says that the apostles and prophets of the first century were there to teach until the "unity of the faith" and a "complete man." In the same context Paul says in 1 Corinthians 13:10, "when that which is complete is come, then that which is in part will be done away." Once the scriptures were written, we no longer needed apostles and prophets.
Speaking of the Old Testament scriptures, and by extension also the New Testament scriptures, Paul says in 2 Timothy 3:16-17: "All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be complete, thoroughly furnished unto all good works." If we, by being transformed are to "prove" the good, acceptable, complete will of God, then that will would also make us complete. Paul says it is the scripture which does that.
So the perfect will of God is that which is to be found by studying the Bible in its entirety. There is no one scripture that states it, but the totality of scripture.