you have to compete in a redbull competition and place top three. start practicing buddy. don't think your going to get one without earning it. only posers do that, just like little kids buying bell bellistic cedric gracia helmets...
The public is unable to get any Red Bull clothing or accessories such as helmets. However, ebay does have a lot of Red Bull hats up for sale but they normally go for upwards of $150US. If you want a helmet similar to the Red Bull ones, I suggest giving TLD a call as I am sure their artists can do some graphics up and replicate it. All you need is a spare $1000+ to cover the paint job and provide any white helmet.