After his untimely death,
a collection Hans Bekic's papers were published as
Programming Languages and Their Definition: Selected Papers of H. Bekic
now available as a
scanned pdf.
For citation info see
here.
I also edited a collection of Tony Hoare's papers - now avaiable as one of ACM's "most wanted out of print book": link is here.
Two papers that relate specifically to the development of VDM are:
Scientific Decisions which Characterize VDM
The Transition from VDL to VDM
I have also co-organised two history events for the
Computer Conservation Society:
Program Verification and Semantics: The Early Work
and
Program Verification and Semantics: Further Work.
The librarian at Computer Science, Manchester helped me pull together
a list of references when I first took a look at the history of formal methods;
it needs updating but might be of some use:
PDF
is a copy of
UMCS 92-12-2.
Three Festschriften in which I've had a hand are:
Brian Randell
Tony Hoare
Dines Bjorner and Zhou Chaochen
See also Semantics Library.