Funding for 3blue1brown comes mostly from community support through patreon. The patreon community has also been a great source of early feedback on videos before their public release, especially while working on "Essence of" series since I hold off publishing those until the full batch is done.
While patreon is a pledge-per-video model, some people have asked about one-time donations. I am, of course, more than happy accept such contributions (links on this page), but know that the consistency of Patreon has been extremely helpful in scoping out future projects and expansion.
I also run a podcast with Ben Eater and Ben Stenhaug. We talk about mainly about education, but are happy to get sidetracked on other interesting things.
More than anything, I just think both Bens are unusually thoughtful and fun to interact with, though in two very different ways, and I think you'll agree.
Want to show your love of math and support of the channel in a more tangible way? Don't worry, we got you, there is a store with some shirts, posters, and coming soon there will be some adorable plushie pi creatures. I have mine already, his name is Randolph, and I love him like my own child.