OK, got it. I had looked under "Transmission" but somehow missed it. Too many gears in that image, I guess.
For future reference, the old part number is 90215-30233 but has been superseded by 90215-26241-00. It has only two locking tabs so I recommend replacing it. Unlike some other bikes I've had, there are no "unbent" parts of the washer to utilize.
Most online stores seem to charge quite high delivery rates for a single washer that fits into an envelope, so I guess visiting an actual store is both quicker and cheaper.