I have just spent a frustrating few hours on the internet hoping to find a picture of a part of the scroll Caesar wrote his Wars on. I didn't expect to find such a pic guessing the original text is long gone. But when I tried to trace my contemporary translation back, I got only as far as a few guys in the 19th century and later, who translated 'the Latin' into English, but nothing about where their source Latin document came from, and so of course no info. on where that doc. came from, etc. So...
What is the earliest know copy of the Wars, and what about it?
Is there a place on the web that will tell me what this earliest doc was, who wrote it, what it is supposed to be a copy of, when was it written, etc?
What you are reading is a translation of a compiled text created from a number of extant Latin manuscripts. Here is a reproduction of the stemma codicum (the reconstructed tree of how the manuscripts were copied from each other) for Caesar's Civil Wars, and any decent critical edition should have the same. Your Penguin copy is probably a reprint of an earlier translation, and either should have a note as to which critical edition of the text was used. From there, you can check that edition, which should give the stemma for the edition.
It would be highly unlikely for you to find any pre-Carolingian manuscripts - in fact, I just did a quick search of the Codices latini antiquores, a list of all known pre-Caroline manuscripts, and found nothing.
You might also find this article on textual criticism intersting.