The most common and most likely answer to this crossword clue is the 9 letter word ORIGINALS
O
R
I
G
I
N
A
L
S
Buddy explains!

The straight part
We know that "Sources" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sources = originals.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ORIGINALS mean?
ORIGINALS noun- An object or other creation (e.g. narrative work) from which all later copies and variations are derived
- A person with a unique and interesting personality and/or creative talent
- An eccentric