The eggs you have of that species are either Old or Spoiled. If you toggle the quantities under Old or Spoiled, you should see a number other than 0. You will still need to enter a price for all three states (Fresh, Old, Spoiled) in order to list that egg.
Yes, I have this problem also. I have 1 Quelis egg (FRESH) and it doesn't show in the Egg Market. It Shows in the list of species but it claims I have 0 eggs.