Problem w/ websites besides Ebay is that you have to do a cash/carry arrangement to get much protection against fraud. Ebay's not perfect, but it's something. The odds of you finding a website with enough mowers to give much selection, while also being local to your area, is slim. I personally wouldn't send money off and hope someone ships me a mower unless I had protections like Ebay, Paypal(marginal ones) or COD gives you.
machinefinder.com. They have a search feature so you can narrow it down by different categories, such as brand, type, price, etc. Also, they do the location thing, so you can search within 20 miles of you, or 2000 miles of you. It's pretty cool.