A TV company pick some people at random (Think Willy Wonka's golden tickets, and stick them somewhere to film them. A house would be too Big Brother. How about a business? Put on a farm and told to run it. A tourist attraction? Campsite? etc? Or just dropped in the woods somewhere. You don't even need to keep the TV company going. Just use it as an excuse to get the people together then the company could go bust and leave them to it.
Or you could do the old 'long lost relatives leave something in their will to various people'.
There are lots of ways to get random people together.