It's possible that:
* You've misheard or misspelled the name. Perhaps you're thinking of a different breed of Angus cattle or a specific farm or ranch that breeds Angus cattle.
* It's a unique, local name. There might be a specific herd or line of Angus cattle within a particular region or farm that goes by this name.
* It's a fictional name. Perhaps you encountered this name in a book, movie, or other fictional work.
To get more information, you could try:
* Providing more context. Where did you hear this name? What was the context surrounding it?
* Searching for information online. Try searching for "Thornberry Angus" along with any other relevant information you have.
* Contacting local cattle breeders or associations. They might be able to help you identify the breed or herd you're looking for.