It's a bit hard to find nylon washers. Ask for M6 spring washers instead. Where do you stay? I bought my washers from a little hardware shop in PJ, didn't buy screws though. And you don't really need to replace the heat sink you could just use back to original one.

Good luck on de XClamping.. (that is what you're trying to do right?)

Sad to hear that you kean RROD. Good luck with the operation, just be very careful when pulling out the clamps and also wathc it so that the washers dont squash anything.