Did you ever find a 7100/7200? I have the RCA Ultimate TV. You can use these with the current webtv dot zone aka Redialed service.
Any old WebTV you can plug into a landline/voip line even. The default 1800 number the boxes dial, all connect to the current WebTV Redialed service for free. You can enjoy the nostalgia of WebTV still, all the old hardware works again. With ultimate tv and DISH, you only can do the web mode stuff, you can't get any LiveTV picture or programming guide data. Just internal box email to email, private usenet network on redialed, IRC, and even news and search works. It converts current articles to the old plaintext html format for webtv to see still.
FYI This works with any WebTV classic unit, WebTV Plus, Dish EchoStar 7100 / 7200, Sony/RCA Ultimate TV boxes, and RCA MSN TV (first one, NOT MSN TV 2)