if it needs to match just the number then the next-to-last token when separated by period chars:
//var -s %a *!*@*.75544455.655456.7654466.ip , %find $gettok(%a,-2,46)
if you have a text file containing these list of numbers, with each on a separate row, then $read can check the file in several methods. In this situation, you're looking for an exact match, so:
if ($read(filename,ntw,%find)) echo -a match for %find found in line $readn
For more examples of using $read see https://en.wikichip.org/wiki/mirc/identifiers/$read
If you need faster access than disk access, you can create a hashtable where these numbers are used to create itemnames, then check to see if the itemname has a value:
//hadd -m jointable 765432 anytext | if ($hget(jointable,765432)) echo -a address match