Cant really understand why you cant find any, must be your looking on the right top lists.
A quick search when i first got into this got me loads of sites.
One thing you will find is that they are all on ### sites, so get a ### program and get the link for a game, Chances are youll find lots of other games on teh ### and you can set them to download wile your away from the computer.
Anyway, heres a top list to start from, any of the top 3 are good, to get you started. If your really into it and have Boradband access like i do, get yourself a ### started up and get some contacts so that you can all share your games.
####://www.top66.com/Dreamcast/index.html
Hope this helps
)
Gallway