I got my Children's Python from Riley's Reptiles (also my Jungle Carpet Python). Riley knows his snakes and is a real pleasure to deal with - he may have just one female left from his 2019 babies. I'm not sure if she is already spoken for; I know she was the last of this clutch to get stabilized with feeding and he recently got her regularly eating mice, so she is either ready to go now or will be very soon. He isn't breeding Children's this year, so if the female is no longer available you'd need to find another breeder - look for folks with positive ratings on MorphMarket or Fauna Classifieds. Some of the Facebook groups dedicated to Antaresia may be helpful, though a lot of those members are our Aussie friends.
Also keep an eye open for Spotted or Stimson's. All of the Antaresia are wonderful. You won't find the Pygmy variety in the U.S. for anything under four figures, but Spotted, Stimson's, and Children's are all reasonably priced.