Whatever Happened to the Twelve Apostles? This, or any other page I read about this subject doesn't give any reference. Where are these stories come from?
Most accounts are tradition from very early on and considered reliable, don't remember the sources off hand though.
I have a concern about one or two of those traditions however. One of them being the final days of Peter.
I'm pretty sure the account comes from the Acts of Peter, and it's interesting to consider Jesus' words to him in John 21, re: outstretched hands.
It is an indisputably established historical fact that St. Peter laboured in Rome during the last portion of his life, and there ended his earthly course by martyrdom. ... St. Peter's residence and death in Rome are established beyond contention as historical facts by a series of distinct testimonies extending from the end of the first to the end of the second centuries, and issuing from several lands. ... http://www.newadvent.org/cathen/11744a.htm#IV Reliable?