Currently, there is no Slack integration to do this.
However, the Fleet team is currently thinking about introducing abilities that may look something like sending the results of specific queries via Webhook requests (that can then be sent to Slack or another location).
Please feel free to file a feature request on GitHub here: https://github.com/fleetdm/fleet/issues/new?assignees=&labels=idea&template=feature-request.md&title=
Including details about your exact use case for this ^ request would be extremely helpful in shaping a future Fleet feature.
As a current workaround, the Fleet UI allows you to run a query against any number of hosts and then export the results as a CSV.