think where they were printed for, the population of those areas, and as such the print run, compared to Quads that were made for the UK.
AND some of these areas had their own posters,
EG look at NZ censor stamps and snipes on UK 1 Sheets, NZ also used Aussie posters, Ive seen Aussie stamps on UK material.
So.... of course there are less, there are less of us, and less posters needed.
I love UK 1 Sheets, the paper quality and print quality is sometimes awesome, compared to US 1 sheets.