Problems using iMac 2009 as external monitor for macbook air 2017
I want to use my old iMac (2009) as a monitor for my MacBook air 2017. From what it looks like online (See link below) I need a Mini Display Port to Mini Display Port cable, and I did buy one online before finding out that it is not compatible with target display mode. Does anyone know where I could find one of these cables that is compatible with target display mode? I did try on the apple store but they don't sell them.
Any help would be appreciated
https://support.apple.com/en-gb/HT204592- This is the link that says i need a Mini Display Port to Mini Display Port cable
MacBook Air