StatBooks has retained Dissolved Companies data since 1 October 2017 and whilst we have no plans to make this available as a front-end module we do the capability to produce and export back end updates weekly or monthly on a subscription basis. There is a degree of volatility within the data due to the daily trickle of administrative and other restorations; we have front-end modules for these (See - LATEST >>RESTORATIONS >>RESTORED >>Requested - NOW ACTIVE / Court Order – For Legal Action on the menu bar).
E-mail email@example.com for more information, specifying the data content and export format requirements.
On a more general note, I would suggest that a total of circa 6.7 million is well below the true figure (we have garnered close to 450,000 in just 10 months!) and a calculation based on issued numbers less the latest total register figure suggests around 8.7 million have been dissolved.