Either flip through an Import Tuner, browse on ebay, or check tirerack.com. I'd go ebay first.
You could get a good, new set of 16's or 17's for around 500 bucks, but you'll pay about 400 bucks for all four tires, like Kumo Xstas or Yokohama Avids. Please pardon the spelling errors. Look for a used set that have no more than 6 months on the tires. BE CAREFUL. You get what you pay for!