You can't usually search for stuff that's already been sold on ebay. But if you know a seller who has sold multiple items you can look through their feedback which lists all the items sold and had feedback on, which will let you see what they've sold.
As of Feb 2008, it was 3.4 billion. That would be about 716,544 items a day since it was founded (8.3 items sold per second). If that trend continued, it would be somewhere around 4.24 billion items sold as of Feb 2011.