make one yourself from some drainpipe and flexi hose... the only slight expense will be a mushroom or angled head if you want it to look the biz. (£20-£30). type DIY snorkel into google, you get a few hits. nothing about actually linking it to the air filter though... make sure yours is on the side of your air filter to limit the amount of hose and poss problems. (unlike mine, which was done by a plonker before i bought my 90). your looking to seal the air filter off and only draw air through the top of the snorkel. so your hose must be perfect and every joint/coupling sealed tight.
hope this helps
G