I find that when a band has a sound you really like, it's often pointless to try and find other bands that sound like them, especially when dealing with a band as unique as Diablo Swing Orchestra. I believe they have a new album coming out soon, so I'd just be patient and wait for that.
However not to cop out completely, another multi-styled band that shares some features with Diablo Swing would be Höyry-kone. I wouldn't say they sound like Diablo Swing Orchestra, but they do have the whole Metal/Opera/Classical/Jazz thing going on.