There is a lot of information and photos of Badajoz on the Frorum. Search 'Badajoz'. This early link mentions several books with maps you might consult. Also photos of recent memorials. The diorama was always difficult to find and may not be there any more. But the walls are still there, including the castle wall. And you can climb onto the exterior, western wall that was first breached by the 30th, close to the river.
You might find the old map on the first page of this badajoz1812 blog useful. The blog is the contribution of young Badajoz historians, the first to seriously interest themselves in the Siege. I took a tour of the battlefield with them, led by Col.Nick Lipscombe. They asked him why the British went berserk, having grown up with the Spanish take on the Siege. He answered that unfortunately the soldiers who had just survived the Siege of Ciudad Rodrigo were asked to go through the same thing again at Badajoz. They wondered if the Spanish were for or against them. http://badajoz1812.blogspot.com.es/2010 ... %20Badajoz
There is a new history museum close to the castle. It houses a diorama of the battle and might have a useful map. On the wall if not in the shop.
You might find the clip on this page interesting. It gives the history of the Siege search.php?st=0&sk=t&sd=d&sr=posts&keywords=Badajoz&start=250