Sounds pretty easy to do, just buy one and drive the crap out of it and then you will have a high mileage GTS.
Sorry, I couldn't resist. Seriously, I will keep my eye open for you. Check ebay, the classified on here, autotrader.com (I think you can sort by mileage, if not by price should pretty much give you what you want) or cars.com. A high mileage car should be a lot easier than a low mileage one to find. Why do you want one with high mileage, are you on a budget? What price range are you looking in?
Mine just hit 1600 miles, I am assuming you are not interested in it?
Before you yell at me for not driving it I just bought it and drive it every chance I get.