On Mturk you upload a spreadsheet of the urls. Set up the "hits" so as to ask the worker to go the url and try to find a contact email. If they find the email they enter it in the "hit", if they find a contact form, they select contact form, if there's nothing they enter in an X or something else, you can decide. For just an email you can pay anywhere between 1-3 cents. For 300 urls you get this done in a day usually. You can put in filters for the quality of workers, I usually keep them pretty strict. You are suppose to go back and check the quality of the workers and approve or reject an answered "hit", though for the $3 - $5 that you'd be paying for this, it's not worth it, just approve all. After the turking you end up with a spreadsheet of all the urls and emails.

Is it possible to setup a turk where an ad is submitted to a message board? If so how?

Thank you

Not entirely sure what you mean. Mturk has an api, a lot of people use it for quality assurance, like checking images for nudity or stuff like that.

I actually just wrote a post about this exact process :)

http://www.supremestrategies.com/get-cheap-guest-blog-leads/

This is a awesome post, thanks for sharing.

I'd assume you give people the blog URL and pay them to collect the e-mail address of the author. Verification could be done by having 3 different people tackle the same blog and checking that the e-mail addresses match. Pay $0.05 or $0.10 per e-mail address and you're set.