Are you looking for snail mail, website, or either? I found this address on the Envoy website:
Catholic Evidence Guild
PO Box 55
Larchmont, NY 10538
It’s the same address listed in the second article you linked to (which is from 1999). The listing on Envoy’s page is from issue 4.6, which came out around the year 2000, so that might not be current. I tried searching under the address at both whitepages.com and yellowpages.com and nothing came up.
Is this the old thread you were talking about? Patrick Sweeny (the OP of that thread and speaker for the CEG) has his blog (Extreme Catholic) in his signature. It appears that the blog is still active. I think it might be against forum rules to post his email address, but it’s there on his blog. You could try emailing him as he would probably know the most recent contact info.
He still has the catholicevidence.org website in the links on his blog. Maybe the website is just down temporarily. :shrug: