I would not ship eggs more than 2 days old, because they are going to spend time in transit. They hatch best when under a week old.
I keep a small flock and I am certainly not the only one. In order to ship you 2 dozen eggs less than 48 hours old, it would be necessary to keep at least 3 dozen hens, maybe more, because there is no guarantee that every hen will lay an egg a day just when I need them.
36 hens plus several roosters for them. That's a lot of chickens to be feeding all year round just to be able to send out larger orders of hatching eggs every now and again.
And then, what if the breeder wants more than one breed of chicken, or more than one color? Now you are talking about a whole bunch of chickens and even more breeding pens, which cost money.