[RajatPawar]

pawn Код:

new File: my_FILE, 
      str[15],
      temp;
for( new i = 0; i < MAX_FILES; i++ )
{
     format(str, 15, "file_%d", i);
     my_FILE = fopen( str, io_read );
     if( my_FILE )
     {
           temp = i;
     }
     else continue;
}

MAXIMUM INDEX  =  temp;

I think something like this COULD work? I am not too experienced with files, TBH.