I'm planning on buying the ear grommets from mcmaster-carr (part no 9311k89) but cant find the shoulder bolts on their site. Anybody know the part number?

I don't know where you can get the bolts but I think you may want the 9311k138 and not the k89. The k138 is the blue one that is shown in the EARS website as being use for HD. I think you shouldn't have any problems w/ using longer 6-32 screws just make sure you don't screw it all the way.

Icefire's correct: you want the 9311K138 grommets.