If you want an exact match you can contact Zotac and see if they will give you a part number or send you the part.
That GPU is a little new to be needing a replacement, but you can also try your luck on places like ebay. Just enter the name of the card and replacement fan, usually someone selling something.
Myself, I would just replace the entire shroud with a pair of nice static pressure fans. Or water cool it with a universal block or all-in-one adapter like the NZXT Kraken.