I don't know of any, but it wouldn't be too hard to create. For about $150, you could hire a developer with Flex & PHP/ColdFusion/perl skills to create the script for you. One thing to bear in mind is you will need a server with Flash media server or Red5 installed on it. Red5 is open source, so if you wanted to sell the script on to others, they would probably want a solution that works with Red5 so they can save themselves about $1000 on Flash media server.
iborg you are quite close to the answer. You should check my blog for a riddle on chatroulette cloning http://flashontherocks.com/2010/03/09/8/
From what I read Chat Roulette uses P2P streaming with RTMFP, not RTMP. There are many clones for this. Latest released is Chat Roulette Clone Script.