Ka I would presume any publishing rights reverted to the authors long ago. Since there's clearly money to be made, it's odd that no eBooks have been released. Has anyone tried contacting either/both of them to ask the question? I'd say that's the best bet for an answer.
Patric I've tried to contact the publishers on Twitter but didn't receive any response at all. Also searched quite extensively for one of those mentioned by Michael Mullins but wasn't able to locate one either.