Advertising certainluy needs to be integrated into a wider startegy. The gambling market is quite packed with sites and it is technically simple to setup a new site and create content is not really expensive, so like in the startups it is all about growing fast and growing cheap. You cannot count on going viral, so you would do best in finding a niche that can be reached by an specific campaign and get a foothold with these clietns.
Advertising these days is not an issue. There are so many palteforms and there are so many freelance manger available on freelance website. I would suggest Fiverr being bestest of all because I work there and its very secure and have good CS as well. You can choose from variety of available resources there.