Most spec scripts for TV start as work-ups of an old or existing series. Most of the formatting rules for movies also apply for TV. Half-hour TV comedies, for some odd reason, follow a different set being double spaced. You can find TV scripts on the internet in different places. Often you can write to a TV production company for their spec guidelines--if you wanted to write on spec for CSI, etc.
Ray is right in that you couldn't sell the series as your own. However, sending a script off on spec is not out of the question. However, if it does catch someone's attention, you probably won't get any acknowledgement ($).
Because most large agencies CBS, NBC, ABC, etc. run their own shops, it is difficult to sell them a series from the outside. It's easier to piggyback as a writer on one of their existing series, build up some credit (and connections), and then try to sell the idea.
There are many planned re-vamps at the moment in development. Bewitched, someone mentioned "Beverly Hillbillies", "I dream of Jeannie" and "Gilligan's Island". It's not that there's a lack of creative writers, just execs like to stick to what's worked in the past. Unfortunately, I don't think the same audience interest exists. It invites a lot of comparison which is often unfair.
In finding older TV scripts, you can put in your search engine "CSI scripts" and you can usually track down a couple. The only caution is that there are 'spec scripts' and 'shooting scripts'. The shooting scripts often have details of camera shot and angles that you wouldn't include in a spec script. It's instructive to see both. But if you do submit a spec script, realize it should not include shooting information.