Another option is to import ready-made blocklists if you aren't already (https://fedi.tips/importing-ready-made-server-blocklists-on-mastodon/), but this may not line up with instances that are hosting spammers because it seems a lot of the problems are with otherwise well moderated instances that have open signups instead of approval signups.
It's the open signups on other instances that seems to be the problem. If everyone had approval mode on, spammers would find it much harder to exploit smaller instances.