Although written specifically with environmental translators in mind, Abigail Dahlberg gives some good pointers to all of us on where to look for clients:
(1) Big players outside your field who need your expertise in that field.
(2) Providers of services in your field
(3) Consulting firms, trade journals and research institutes in your field
(4) Government institutions
(5) and finally translation agencies
There is some more good advice in her posting.. like reading trade and professional journals to get an idea of who is doing what that might need your translating skills; attending trade fairs, and talking to other colleagues about what you do so they know who to call when they come across a good opportunity.
Do read it in full.