Google "donating Kindles" followed by your county, major city or state. Many school districts have a donation program for schools - kindles given to kids whose families can't afford them. There is also this one:
https://www.developafrica.org/donate...schools-africa
I've been donating my older units or units others give me to senior citizens because they can make the text large enough to read. Contact senior housing, Assisted Living and such places - usually the activities coordinator would know if they can use them for a resident. Most residents download from the local library system, so they do often have to be usable for that.