Where can I find a graphics card for this mac?

Hi guys!

I have my mid 2011 21.5” iMac and I am in the process of replacing the graphics card, I’ve been looking around to try and get one without paying a whole lot, all the ones on eBay seem to be rather expensive along with shipping around the same price as the unit, as I live in New Zealand but still shipping should never cost that much.

Do you know where I would be able to purchase one of these cards for a bit cheaper or without as much shipping cost!

Thanks.