Search on ebay for "nikon fe2 eyepiece". There are about 20 showing up right now and about 10 of those offered are 0 diopter lenses. The ones marked as "replacements" or 2925 are actually -1.0 value. That is the Nikon Stock eyepiece for those finders. You can easily compensate for a +-1 or .5 with the diopter adjustment on the D7K.
That lens, plus the DK-3 rubber eyecup and the DK-22 adapter are the 3 items needed for the all-Nikon eyecup.
There are alternatives available (especially on ebay), but you get what you pay for, so to speak.