Is it the brace that you're looking for a part number on? If so this looks about right. The view in the picture is from the top but the ruffle pattern along the edges and the placement of the holes look right.
Part #: 74870-1EA0A
Name: Nissan OEM Undercarriage Body Tunnel W Brace - Nissan 370Z 09+ Z34
https://conceptzperformance.com/Cart...n.php?II=17265