Well I don't know if there is any actual device you speak of, however I found a Ben Heck mod that changes DVD's via an old Sony 100 disc DVD changer.http://www.electronista.com/articles/11/07/11/ben.heck.makes.a.100.disc.changer.for.xbox.360/
I know it's for an Xbox 360 - but I still think you could possibly modify it for a computer. There still might be some manual clicking - but at least you wouldn't have to manually change the DVD.
.....or hire a summer/college student to do it
Edit: Actually found more information. I believe what your looking for is an autoloader:
Check this link out first:http://www.meritline.com/dvd-autoloader---c-7776.aspxhttp://www.mfdigital.com/automated.html