I see that you're in Minneapolis. You can start by contacting the local collector club. Someone there may have what you need, or have local connections to someone else who does:
http://www.northlandantiqueradioclub.com/
You could also try the Pavek Museum of Broadcasting in St. Louis Park:
http://www.museumofbroadcasting.org/
Again, what you're looking for is someone with
connections, who can help you find what you want.
Unless you're already experienced with restoring old TVs, your chance of finding something at Goodwill and getting it working by yourself in a week or two is zero. Fixing old TVs takes more than just popping in a couple of new tubes. If you flip through some of the TV restoration articles at
http://antiqueradio.org/restoration.htm , you'll get an idea of what's involved.
If you want the TV to play at the party, be sure to specify that you're looking for a TV that is already
fully restored and reliable enough to play in public for a few hours. An unrestored TV will not be reliable (if it works at all), and might go up in smoke at any time.
Since time is short, I'd pick up that old fashioned device known as the "tele-phone" and call these places, rather than send email.
Phil Nelson