Instead of finding the matches of the text you want as the result, it may be easier to replace the stuff you don't want:
>>> import re
>>> x = "From: Joyce IP: 192.111.1.1 Source: 192.168.1.1"
>>> re.sub(r'\w+:\s', '', x)
'Joyce 192.111.1.1 192.168.1.1'
However, if you prefer to use re.findall() here is one option that is similar to your current approach:
>>> ' '.join(re.findall(r'(?<=:\s)\S+', x))
'Joyce 192.111.1.1 192.168.1.1'
You need the \s in the negative lookbehind because there is a space after each of the colons in your input string.