Where to get replacement plastic pins for iMac GPU heatsink

I was working on an overheating iMac 2009, and when I came to looking at the GPU’s heatsink; the spring-loaded black plastic posts holing the heatsink onto the GPU both cracked…

I’m guessing they were made brittle by the excessive heat of the poorly cooled GPU ( I noticed the thermal paste was cracked)

My question is: where on earth can I find/buy replacement spring-loaded black plastic posts to fit the heatsink back onto the GPU?