I'm just going to tell you straight out none of these people here are going to be able to get you 500,000 real followers per month. 5,000 now that's attainable.
I specialize in Twitter Marketing strategies and have used free tactics of promotion in all of my online businesses.
Basically I just have a trick that I use that will gain hundreds of new followers per day that are in your niche and I have another trick that I use to test sales pages, free giveaways, and even just regular blog content.
I would be happy to do this for you on an on going basis.