The entire sequence of Lange's photos are available for download from the Library of Congress here:
https://guides.loc.gov/migrant-mother/images
The FSA photos are considered the property of the citizens and are free to download and use without cost. I have a copy of Lange's photo along with several other FSA photos hanging on the wall of my home. Most of them took a bit of cleaning up in Lightroom but it's worth the effort for the history and art.