An Episcopal church in St. Louis has started a collaborative effort to fund rebuilding the damaged churches. In addition to soliciting donations from individuals, they're asking congregations of all kinds to take up special collections for the cause. Info is here:
(Thanks to mactavish for the links.)
Please donate if you can, and spread the word, especially to community leaders who can organize larger collection efforts.
If you regularly read or watch the news, and you haven't seen any coverage of these events, write letters to your favorite news organizations and ask them to cover the fires (ideally using the words "arson" and "terrorism") and to signal-boost the fundraiser. Make sure to mention that you're a subscriber or frequent reader/viewer.