They don’t exist anymore. The oldest OT books we have are the Septuagint, which was written in Greek in Alexandria Egypt because Hebrew was dying out (or so they thought) because of the babylonian and assyrian exile, which caused some of them to flee to different areas. Because they were spread out, they were “assimilated” into the Greek culture (Early Roman empire spoke mostly Greek, which covered Alexandria).
The Septuagint is even used to correct the oldest Hebrew versions that we do have. The oldest Hebrew OT texts that we have date back to around 600 A.D. I believe, whereas the Septuagint dates back to 250 A.D., even though it was first penned around 250 B.C.
Even St. Jerome complained about not having the original Hebrew texts, which is why he had to use the Greek versions for parts of the Vulgate (around 400 A.D. I think, which is when the canon was officially closed by the RCC).
We know that the Septuagint was used in and around Palestine during the time of Jesus and was widely accepted among Jews (still used among ethiopian Jews today). Only after Christianity became big did the Jews reject that canon (around 90 A.D. some estimate), even though it wasn’t really a canon then. This was because Christians had constant recourse to it and the Jews wanted the old Hebrew texts back, which they had back then. The rejected books were, of course, books written B.C., Jewish OT books, such as Maccabees.
On the other hand, the Dead Sea Scrolls (Discovered in 1960’s in caves near Qumran near the dead sea) do provide us with some Hebrew and Aramaic texts, but they are somewhat sparse (I saw a bunch of psalm stuff). Interestingly enough, the dead sea scrolls do contain some of the books that the modern Jews removed and the non-Catholics removed (because they believed that the Jews still had authority over scripture), but which Catholics still keep in their bibles today because the RCC said they are good and true, and they have that authority now, because it was transferred by Jesus.
This is what I remember, but I could be incorrect on some details.