Not in the exchanges business.
In my opinion, You need to formalize the notion of a "good copywriter" and requirements.
For example, a good copywriter:
— Experience in copywriting N years
— At least X publications on it subjects
— The average uniqueness of content is not less than Y% according to such a system
The tasks will include:
— Publication of at least n of materials per week
— The volume of one article about y thousand characters
— Sources of articles for foreign publications, rewriting, content
Payment terms are.
Possible career growth to the editor of the portal or something like that.
Then posting on any popular stock exchange this offer You will receive about two dozen proposals. And we need to filter, communicate with each author separately, if you want to find a good person on a long term basis. I recommend a voice chat via Skype, for example, better feeling, speech can understand how he thinks he etc.
If you go back to exchange, I recommend free-lance.ru because You need a man, not a specialized type of exchange Advego, where the objects are texts, not people. IMHO