Here are some things to try to discover. A word search of πέτρα would also turn up Ps 114 (LXX 113):8. What are the two Greek words that are used in this text to describe the rock?

The πέτρα search would also turn up WisSol 11.4. What words are used to describe the rock here?

Search for πέτρα in Philo. (This can be done easily in BibleWorks.) There are not many references, but look at the one in Allegorical Interpretation (=Leg) 2.86. What words are used to describe the rock and what else is said about this rock?

Look up how Numbers 20.8-13 is translated in the Targumim. In BibleWorks, use the PJE version. Online you can check it out at: http://www.tulane.edu/~ntcs/pj/psjon.htm  Especially note what the Jerusalem Targum records. (It is embedded in the Pseudo-Jonathan text.)

Using the index of the Old Testament Pseudepigrapha online at: http://www.bombaxo.com/otp_index.pdf  , find a reference to Numbers 21.16-20. (Note that LAB = Book of Biblical Antiquities = Pseudo-Philo) When was this book written and where? Check online at: http://www.earlyjewishwritings.com/pseudophilo.html  Now look up the reference online at: http://www.sacred-texts.com/bib/bap/index.htm  . Be sure to read the footnote to the verse.

Now see what Ginzberg records in his Legends of the Jews online at: http://philologos.org/__eb-lotj/vol3/contents.htm  Read both the sections on “Miriam’s Well” and “The Waters of Meribah.”

You should have a fairly clear idea by now that the “following rock” was not an innovation by Paul. But why does he claim that the rock πέτρα is Christ? Let’s see what you can discover within the NT that might support this claim!

As a reward, now go to e-Catenae of the Ante-Nicene Fathers at: http://www.earlychristianwritings.com/e-catena/  . Look up the links to 1 Cor 10.4 and find what Origen in his Commentary on Matthew says.

Still with all these resources, you would miss one final nice one that you could discover by searching for πέτρα in the ANF of BibleWorks, but I’ll give it to you straight: http://ccel.org/fathers2/ANF-03/anf03-49.htm#P11569_3266884