You have a password policy with special chars, you have rate limit, you want to know the most common special chars in passwords.

rockyou_stat.py

import re
from collections import defaultdict

d = defaultdict(int)

with open('/usr/share/wordlists/rockyou.txt', 'r') as f:
  for l in f:
    for c in re.findall('\W', l[:-1]):
      d[c] += 1
      
print sorted(d.items(), key=lambda t: t[1], reverse=True)