Before you get too excited, this is limited to 2 connections, 10 day retention, and 2mb download speed.
As for the 10 day retention, I've just tried part of a file from 2011 and it's downloading. I'm using Grabit (free), and it all seems to work.
Here's the page to sign up for a free account (with option to buy an upgrade, but I would stick to free).
https://www.xsusenet.com/
Hitnews 3 day unlimited Usenet. Just sign up with a username, password and email account, no payment info required. It might take a while to activate your account, possibly half an hour. You can keep signing up again and again, but you'll need a different email each time.
I recommend this as it's full speed and high retention.
http://www.hitnews.com/