Harry,
I don 't know any suppliers. Sorry, I can't be of help with that. I am writing because I am curious why you want individual ocular lense caps. Can you explain?
I have always preferred to have a rain guard, what you are calling a "one piece eye piece cover." It serves better to protect the oculars from rain drops, pollen, detritus,etc in the field. It is easy to put on and off once it is attached to the strap, thus protecting the lenses while walking, eating, drooling, etc, while still being quick to remove when a mysterious bird flies over. When not in use, I put my bins in their case with rain guard on and that works fine protecting them in storage.
Whenever I have received a new pair of bins with those individual ocular caps, I have been annoyed. I have done almost exactly what you are doing, except I looked for an after-market rainguard. I think that more and more bins for birders are being supplied with rainguards in place of ocular caps because most buyers prefer them. So I am especially curious why you prefer the individual caps, since I have never seen any advantage to them. But, I am probably missing something. Please enlighten. Thanks.
Marc