Hens like to hide their nests.
Getting twelve eggs to enter in a show or fair is difficult. The eggs should be uniform, and of the same color and size. One of our best laying hens always eats or claws up the eggs she lays. Some of the others hide their nests. If you are in this situation, the only way to get a good dozen eggs is to start saving them at least a month before you need them (the only way to do this is to refrigerate the eggs.
By the time over a month has passed, the eggs may not be good to eat. But that doesn’t matter, since at most fairs the eggs are judged on appearance, not taste (there may be exceptions). Just be careful that you don’t break any of them, or the smell may not be pleasant.
Some hens will eat their own eggs.
To get the eggs looking good, we have found that it works best to was the eggs the day before. We take a paper towel soaked in soapy water and scrub them off. Usually you can scrub calcium deposits off the egg if you want to.
Once you have saved and cleaned the eggs, you need to sort them to pick out the best ones. Usually it takes a lot of eggs to get a dozen good ones.