Is there a way...

[Marcus Telcontar]

I can find out the last IP address a person posted from when that IP address is NOT in the forums I moderate, or for a given date / time range?

It,s the date / time range that would be best for what I want to look at.

[TheHolo.Net]

You can request it from an admin stating your reasons for doing so and the admin will decide whether or not to provide it to you dependant on the request. IPs in forums you do not moderate do warrant at least some privacy unless there is sufficient staff moderation need requirements to aquire it.

It would also help for you to provide the exact post you need the IP address from. Using the "find posts by this user" link in their profile is handy for finding specific date/time range posts.