import re
text = "1. Notice \nSome text \nEnd Notice\n2. Blabla \nSome other text \nEven more text\n3. Notice \nSome more text\nEnd Notice"
pattern = r"^\d+\. Blabla.*(?:\n(?!\d+\.).*)*"
result = re.findall(pattern, text, re.M) 
print(result)