The Flakpanzer IV was, apparently, a pretty rare beast, and my library isn't really late war heavy, but William Auerbach's Last of the Panzers (Arms and Armour, London, 1984) came up with the goods again:
A clear view in the photograph above, with another Wirbelwind, very ominously damaged, below:
Both these were taken on the Western Front in early 1945, and Auerbach notes that only 86 Wirbelwinds were built (using reconditioned Pz IVs). Given this, and the obvious anti-ground attack role of the Wirbelwind, I'm beginning to wonder if it only served in the West. If so, that's a nuisance, as my late war armies are all orientated to the East. Blow.