Did some research:
If we are talking about grants strictly for UI/UX design: I didn’t found one and I don’t think there is one. This topic is probably not attractive for potential donors and various foundations.
Maybe we could add this to one of more general opportunities (like Cisco Grant), but then we would need then to show how UI/UX redesign would help people in need and show it’s social value. Most important, we would also need budget (not specific, but more or less) for this before writing any proposal, just to know if we can fit it into various grants limits.
If we are talking about organizations, there are some design non-profit companies that are specializing with work for social good projects. Still, their work isn’t free, just about half as expensive than services from traditional companies. I’ve found only one organization, that offers help with finding funding for their work - IDEO.org. I’ve filled out their contact form from website, if there’s gonna be any feedback from them, I’ll let you know.
There are some websites that are connecting specialist (also UX/UI ones) with non-profits for volunteer work, if you are interested, we could try posting requests on them.
Not sure if this helped, if you have any questions, let me know.