You're going to have to physically take the cooler apart until you reach the thermal pads, measure their dimensions, thickness, width and length and then buy the pads accordingly. Not all cards are made the same due to an aftermarket cooling solution varrying from one AIB partner to another.
Now would also be a good time to understand how to disassemble(and in that process, reassemble the GPU).
Answer: Measure, measure again, write them down on a piece of paper and then order!