I Looked Into This A Few Months Ago & Found A Couple You Might Be Interested In. First One Is Pretty Basic, Second One Has Alot More Features.
http://www.phponlinedatingsoftware.com/index.htm
http://www.abk-soft.com/
I Have A Couple Dating Domains I'd Be Willing To Part With If Your Looking
myesingles.com
singleandlookin.com
Hope It Helps