Your question is confusing. You 'seem to find a regular anti spam script' that does exactly what you want it to do? Awesome then!
There are a lot of repeat text scripts and approaches out there. Except you probably want more than just that, since people immediately evade the script by subtly changing each line of text. mIRC doesn't have a built in string comparison or similarity hashing to determine when two sentences are 90% the same. So it quickly becomes a cat-mouse game and very lengthy script.
[ Anyone out there want to find and write a similarity-hash that produces N-bits (ie, 100 bits) of string fingerprinting, so that two or more hashes can be compared to determine likeness based on bi-grams, simple bit masking or string sort? ]
Well. At least I won lunch.
Good philosophy, see good in bad, I like!