Is there such a thing as...

I can't say for sure, but I doubt it--it would have to be able to cross convert from Digital to Analog signal which would generally require some electronics to handle that processing.

This should help:

http://www.hdtvsupply.com/hdtocoad.html

Do a search for visionfc4. It's pricey but it is suppose to do what you want.

Technically, these things are called transcoders, I think, not adapters because of what Kjweisner said. Run a search on HDMI-component transcoder. There are some available on ebay
but remember, since its an active device, you will need to get one w the proper input and output. Most of these are not 2 way devices. Key digital is a good manufacturer.