NB a few organograms have been released in other ways, such as PDFs from 2010/11, some lingering RDFs 2010-2016 and the occasional CSV 2010-2016 that didn't go through the data.gov.uk system. Many of those are listed in data.gov.uk datasets alongside the ones that have gone through the system (and a few are just on https://www.gov.uk/government/publications ). So this is not complete, but not far off.
NB this dataset doesn't contain the actual organogram data - it is just a list of the releases and the URLs to get the data. This is helpful to understand how well government bodies are meeting their commitments.
listed at https://data.gov.uk/apps
This is exported from data.gov.uk's database. It is refreshed nightly.