For those of you that like the feel of a REAL eyecup, there is an old-school "oversized" one that fits perfectly. This particular eyecup is from Nokon, but has no specific model number. They are readily available from various sellers on eBay, which is where I found mmine..
Being used to the older eyecups that actually served a purpose, I was pleased to find these, and it's made a world of difference for me!
I have not used the following photo store, but they have a pretty good online catalog of Nikon accessories. Does it appear there? Perhaps Rubber Eyecup II or (there's also a generic version) or maybe #2939?