Matt. 27:9-10 quotes a prophecy made by Jeremy the prophet.  Yet, no Bible believer has ever been able to show me where it lies in the Book of Jeremiah.

It is no wonder the Bible sometimes causes confusion.  We come with preconceived notions and draw consequent conclusions to issues that can be fairly easily addressed otherwise.  The most immediate simple answer here is to decide whether you believe that all the prophecies of Jeremiah are contained in the Book of Jeremiah that we have in scripture.  There are diverse places in the bible where extra-biblical literature is quoted.

There is also the fact that some versions of scripture have the prophet as Zechariah or Isaiah.  Can't find the verse there?  Well, you have the same question to answer, "Are all the prophecies ever delivered by any prophet contained int he respective biblical book?"