I haven't seen any but, As we have power of the entire universe(in short we are developers). Use their developer API and create a small tool. The API is very descriptive,
Additionally, there's a box that is golden. Uncheck it to not automatically be set to watch all repos you're given push access to. Hooray for managing the signal to noise ratio.
I'm not a fan of command-line tools that want my password in plain text on the command line (thus visible to all system users who run 'ps' at the right time, and also stored in plain text in ~/.bash_history unless you take extreme care to avoid that), so I haven't tried it.
I know it's a bit late but this might be handy. The proposed solutions are little complex & few solutions doesn't allow you to specifically select an organization, etc.
# Make sure the personal access token has access to notifications & repo
GH_TOKEN=<TOKEN-HERE>
ORGANIZATION=<ORG-NAME>
MAX_REPO_COUNT=5000
repolist=$(GH_TOKEN=$GH_TOKEN gh repo list $ORGANIZATION -L $MAX_REPO_COUNT --json name --jq '.[].name')
echo $repolist | while read repo; do
echo "Unsubscribing from $ORGANIZATION/$repo\n"
GH_TOKEN=$GH_TOKEN gh api -H "Accept: application/vnd.github+json" /repos/$ORGANIZATION/$repo/subscription --method PUT -F ignored=true | jq '.'
done