The best way to find freelancers may be to ask for referrals. But if you're not in a position to do that, Elance may be a good place to start looking. I've been working via Elance for seven years. Once I hit the Top 10 in the Writing category, I started to get a lot of referral work from my Elance clients, and became significantly less active on the site (So, Dave was right.) Nowadays, most of my copywriting and marketing strategy work comes from word-of-mouth, but I still do an occasional project via Elance because their escrow feature can be handy.

As to the portfolio question — let's say you're a mortgage broker and you've just paid a copywriter to create a $10,000 sales letter for you. Would you want that writer to share your letter with the next mortgage broker who comes down the pike? Of course not. That's why most clients insist on non-disclosure agreements. That's why I can't share most of my portfolio with you (as much as I'd love to!)

You may be more likely to get samples if you ask to see work that's unrelated to your niche. That way the freelancer has some confidence that you're not just going to steal the content and use it for yourself (this is an extremely common scam on sites like Elance.)

It doesn't have to be in your niche to be a good source of information. When you're trying to evaluate a copywriting or design sample, you need to know who the target audience was, what the business goal was, and what the results were. That's true for any niche.

When I'm hiring someone, I put a lot of stock in testimonials and references. As a freelancer, I actively solicit them from clients, because they're so much more effective than any marketing copy I could write about myself.

I hope that helps. If you need more tips for screening applicants on a site like Elance, or need help writing the kind of project description you need to attract top talent, please don't hesitate to give me a call.