Our community is now set up on
Linen, a(nother) tool that makes our public Slack history searchable.
Take a look:
https://linen.futureofcoding.org/c/thinking-together
There are some design decisions behind this tool that make it not-quite-ideal for us (eg: while it does index all our public channels, it only displays posts that have replies). But I'm actively talking to the main dev, and they're doing a lovely job of tweaking things and planning changes that would make the tool better for how we use Slack.
I'd love for you all to kick the tires on this and see if it suits your needs. Let me know if you have questions / feedback for the dev, too.