Of course the RasPi composite video doesn't include sound. Composite video never does. It was broadcast on another frequency, usually 5.5 or 6 MHz above the video carrier, so any modulator with sound will have two inputs.
I found a bunch of RF modulators at amazon.com. Just search for "RF modulator" in "Electronics". I think it's video game consoles that keep them manufactured -- when you replace the family CRT with a nice flat-screen, give the kids the old CRT to use with a video game console.
If you use RasPi, make sure you get one with audio inputs since its composite video doesn't have sound.
Max, @Betajets's suggestion of using an RF modulator is good - you can then feed ANY video output from anything (you can even get PC cards with video outputs) to your TV.
If you can pick up a defunct VHS recorder (another visit to Mock?), they usually have an RF video/sound modulator in them and you can adapt them to PC or DTV Set-top-box outputs - but it will probably involve a bit of getting your hands dirty. And since Australian video standards are different from yours, you won't be able to send it to me to fix :-) though most TVs these days are multi-standard.
You may be able to buy something which has video/audio inputs one end a a VHF feedout the other end, I'm not sure where though....
This should work: Get a Raspberry Pi and run Raspbmc (Raspberry Pi Media Center, www.raspbmc.com). Put RasPi's composite video and stereo audio outputs through an RF Modulator to convert to VHF channel 3 or 4.
You forgot to sign up for your free digital TV converter box. http://www.dtv.gov/
Actually I think you should use it as the head of your robot avatar. Then it could roam the halls with the image from your web cam.
I am not sure if you will be able to identify your model here without actually visiting, but you may find the MZTV Museum of Television (in Toronto) (http://www.mztv.com/) of interest. The new site doesn't seem to have a link to pictures of some of the TVs so try the gallery on this old one (http://www.mztv.com/newframe.asp?content=http://www.mztv.com/moses.html).
I got to see an exhbition several years ago during "Doors Open Toronto" and it was fantastic.
Replay available now: A handful of emerging network technologies are competing to be the preferred wide-area connection for the Internet of Things. All claim lower costs and power use than cellular but none have wide deployment yet. Listen in as proponents of leading contenders make their case to be the metro or national IoT network of the future. Rick Merritt, EE Times Silicon Valley Bureau Chief, moderators this discussion. Join in and ask his guests questions.