There are wanted ads in the Marketplace. Go to the Marketplace and go to Engines and Motors. At the top of the page there are five tabs: All Ads, Auctions, Classifieds, Classifieds - Will Trade, and Wanted. Click on the Wanted tab and it will show all of the wanted ads in that category.

When you place an ad you will be asked if you want to place an Auction, Classified - Sale or Trade, or Classified - Wanted.

Eric