Freelance marketing is a much different beast than freelance programmers. That's because, unlike programmers, most people think they can do marketing, without any experience or training. The same cannot be said for programming.

Those that are wise enough to acknowledge that they're not an expert marketer tend to bring the job in-house. Marketing is much more hands on with the business end and I believe people feel more comfortable having someone there day in and day out.

With that said, there are places like elance, RFPDB, and Craigslist where marketers can find work. However I've found that personal recommendations are the best way to go (I know this is obvious).

My experience has proven that these sites are extremely ineffective. People ask for the world at very low pay. Like the many different programming languages, there are many different disciplines of marketing. I'm not sure if programmers are expected to know every language, but many people looking for freelance marketing help expect someone to have expertise in all forms of marketing (i.e. SEO, Social, PPC, Media, Content, Email, etc). Not impossible, but not common.

I'm sure paragraph 3 was all you were looking for, but I thought I'd add in some color to the answer :) Hope this helps.