CPU heat sink screws

[Steve5415]

I recently purchased an imac A1312 mid 2011 27” for £40, I decided to check inside and found that the heat sink covering the CPU has no screws attached to the logic board just the ones with the spring in the heat sink itself, I can’t seem to find the screws that go into the logic board and fit inside the ones in the heatsink, same type that keep the GPU connected to the heatsing…any ideas where I can find some.