http://www.newfriends4u.com/online-dating-service/dating-portugal.html
http://www.algarve-businesspage.info/en/ayp.php?Kat_ID=6&UKat_ID=60
Those links, between them, cover three, and were all on the top half of the first page of results from a google search of "dating agency algarve".
Have fun! :-)
