There are multiple different websites that are targeted at freelancers and helping them find work. Below are of the website we suggest to help you get started on your freelance journey.
Freelance Alliance - enables your to create a profile and portfolio to get you exposure.
Monster - search Monster Jobs for freelance work.
Recruit Media - a source of regularly updated jobs including freelance work.
First Writer - excellent directory of agencies, and publishers as well as writing tips and listings of writing competitions. Entry to the agents and publications listings is a subscription service, but at £2.99 for one month it is worth the money.
Online Content UK - media and related copywriting jobs at Online Content UK
Writers Market - another website that lists agents, publishers and more. $39.99 for a year subscription or $5.99 per month - example listings available on the site as well as a 30-day money back guarantee.
Freelancers Network - mainly IT listings but quite often copywriting jobs appear here. While on the site why not profile yourself?
Guru - project posting and bidding site, easy registration and always some copywriting work here.
More on copywriting as a freelancer.