Originally Posted by Jeff Wills

I think they're almost universal. Once Shimano settles on a working design, they tend not to change it without good reason.

I went looking through Shimano Techdocs, and I think you can use a Shimano p/n Y6K298060, found about 2/3 of the way down this page:
Universal Cycles -- Shimano Road Shifter Service Parts
It's cheaper from Universal, too.