may never find the nest, especially if you have large rocks in the pen. I know DVL here on this forum has hatched many chucks naturally in outdoor pens. Depending on where you are and what type of soil you have you may want to try to mist the pen daily for an hour or so just to keep the soil humid enough so they can get out of the ground Are you sure the chucks have been gravid in the past? Could be they did not produce any eggs. I have a friend in AZ that has some lay in outdoor pens and can usually see the nest spots since he only has piles of smaller rocks in the pens and still even knowing where the nest is cannot find the eggs most of the time so he just mist the pens and most of the time they hatch on their own. Good luck and keep us posted.
Tom Greb