1)Groklaw doesnt' depend on anonymous tips. The site could simply put up a huge disclosure statement on a web form that THE NSA might get what you say. Or not accept tips except via public comments but still operate.
2)Most of the people Groklaw corresponds with don't need anonymity either. Those that do presumably know it and hence, will not correspond with them absent secure means (once made aware of the need for them)
3) Groklaw isn't an email service provider, it's a legal blog/online magazine. As such, likely none of the NSA's mechanisms for getting information from email providers apply. Compelling individuals to hand over their own correspondence is, as far as we know, hard. It can get worse with freedom of the press issues.
So post a PGP key and say, if you really want anonymity, use this.(Edit) and use a mixnet or Pond, or something to send the message. PGP encrypted email from a new account just deals with the NSA's email intercept capability. If you are worried about their other abilities, you need something stronger then Tor since it fails for global passive adversary.
Of course, that wouldn't get them publicity