DISTRIBUTION OF SURNAME 1881
This is the distribution of the 3 main variants of the IS/IZ/IZZard at the 1891 census. As you can see it is mainly a south of England name and remains so to this day
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There are also all variants of the name in Australia, Canada and many in the USA, there are some in Scotland who stem from the Bromley Isards.
I have not found any yet in New Zealand or South Africa.