I have produced a PRC version of 'Clouds of Witness'. Search our Ebook upload section. I have also converted 'Whose Body?' some time ago.
They are out of copyright in countries which operate the 'life of the author plus 50 years' rule. My source was Project Gutenberg Canada. (Canada is a life+50 country.) If you want HTML or text versions of these novels then look there. However, I found 'Strong Poison' elsewhere.
It is possible that more of the novels will become freely available in the future. But the rest have not yet been made freely available, as far as I know.
And if you want 'Thrones, Dominations' then you will have to buy it. It is a continuation by Jill Paton Walsh, and is still in copyright everywhere, because Miss Walsh is very much alive and writing.