http://abandongames.com/
http://dosgames.com/
These sites have the standard list of games that can be legally downloaded (I didn't know Police Quest 1 was legal?)
Other than that, you'll probably have to try looking on Kazaa. It's a slim shot, but it's hard to get old dos games nowadays. Seems like only yesterday (or 1998) you could get any full version game you want anytime. And you didn't have to vote for peoples websites either.