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.