Bonzo312 has analysed a case of Series 5 minifigs and reports that the make-up is as follows:
So there are at least three full sets in each box which wasn't the case with some series 4 boxes.
Now that the Ugly Duckling is not running his website any more, it's harder to track where these are available. They've been in the UK for a couple of weeks (in WHS at least) and in the Netherlands (where Bonzo312 is) and I suspect other parts of Europe, but I haven't heard reports of anyone in the USA finding them yet.
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