well you need to contact a company you think would be applicable to your site. to be frank, your chances are slim unless it's a rather small company as you only have 9 members of the forum and 5 news stories submitted in the past 6 months or so. my personal blog has more activity than that.
look into manufacturers of gaming accessories and other game products.
howeverm don't just e-mail them and say "hay, i wanna know if you wanna do a competition or sumthing at my site for your benefit OMGLOLZ"
you need to come up with a solid plan, or atleast a good outline of how the competition will work, participants, etc. and present it well. anything other than that will likely be completely ignored.