Where could I find someone that would find businesses that want to advertise on my site? In return they would be paid commission, for example 10% of the first month. I know people do this for brick and mortar businesses but don't know how's it done online.
I am not sure, you may be limited to local businesses unless you found someone in the 'partnerships' (I think) forum.
i use elance.com for this type and almost all my freelance needs. just put a job description up. in no time you will have offers. if you are confident in them you can even hire them and once they have a potential buyer, you can add the commission into an escro account through the site. once the deal is sealed, just release the escrow funds to pay them. if you want to interview people face to face, try craigslist but you can always use skype for interviews too. hope this helps.