Its a plugin im writing for strfry (its what the free relay runs on). Just add freelay.sovbit.host to your relelays if you want to use it. Although I am still tweaking with the spam filter.
It won't stop reply guy spam from coming from other relays, but I think I've eliminated the problem on my relay. (I'm saying this extremely conservatively, because while I'm no longer seeing a reply guy spam, occasionally I do see a couple of legitimate posts get blocked, but I think I fixed that with this newest check)