You may not have heard of the Public Interest Registry (“PIR”) but they are the US non-profit behind the .ORG domain name.
PIR have announced that .CHARITY, .FOUNDATION and .GIVES domains are available, and .GIVING will be available later this year.
Aside from a memorable domain name, you might also consider licensing one of these new domains to protect your brand. Either way, you can see their press release at https://thenew.org/pir-now-offers-charity-foundation-gives-as-part-of-org-family-of-domains-portfolio/ and purchase domain licences in your normal way.