I do not know of any online source like that. If there was one, it would probably be a pirated copy of the yellow book. If you are going to invest in more cast iron, it would be well worth it to have some resource books of your own. These are the 3 books most collectors start with, and they are available online:
1. The Book of Griswold & Wagner, Favorite, Wapak, Sidney Hollow Ware by David G. Smith and Chuck Wafford, fifth edition copyright 2010 (referred to by collectors as the Blue Book)
2. The Book of Wagner & Griswold, Martin, Lodge, Vollrath, Excelsior by David G. Smith and Chuck Wafford copyright 2001 (referred to by collectors as the Red Book)
3. The Griswold Muffin Pans by John B. Haussler copyright 1997 (referred to by collectors as the Yellow Book)