I'm interested in Old Latin and was trying to find some texts written by writers like Cato, Ennius, Terence, etc. As I was doing this I discovered that there might not be surviving textual examples of Old Latin other than inscriptions. So I got to wondering: where do all these sources about antiquity come from? Are there a significant number of papyri or scrolls from say the republic or does everything we know about them come from medieval codices? How do we actually know about ancient European literature prior to well preserved vellum books? And finally if you have any good resources about Old Latin I'd appreciate it!
I'm not sure I understand the question. Inscriptions are a perfectly good source of Archaic Latin. Moreover your assertion that there are no surviving manuscripts of Archaic Latin is patently untrue. Though Cato's Origines are fragmentary, fragments of nearly all his speeches exist, and bits of his de Re Militari and other writings exist. His de Agri Cultura is extant in its entirety. Large sections of Ennius' Annales are preserved, and we have decently-sized fragments of his tragedies and various other works. Terence survives in manuscripts of six of his plays in their entirety--the earliest manuscripts are as early as the fourth century, which is wicked old for these copies. This isn't even including authors like Plautus, of whose plays around twenty have survived complete. There's plenty of Archaic Latin...
I found the perfect book on archive.org! "Remains of Old Latin" https://archive.org/details/remainsofoldlati01warmuoft
There's more than one volume: https://archive.org/search.php?query=Remains%20of%20Old%20Latin