Unfortunately mIRC doesn't support searching an ini file like it does a text file (reference /help $read)
To my knowledge you basically have two choices:
1) Use a loop to read the information from each line in the ini file, then see if there's a match.
2) Load the section of the ini file into a hash table, then use $hfind to search the hash table.
Personally I prefer the hash table method, as it is faster, due to the fact that the search is done in RAM, rather than having to read each line from the file on the hard drive.
Decide which method you prefer, then I, or another helper will probably be willing to write it up.
P.S: This sounds very familiar, if you have posted this on other sites, please check to ensure that you haven't already got an answer there.