Yes, Moon is a Harsh Mistress hasn't come up yet, legally.
A number of Heinlein books were availbable, then a batch came available later, then nothing for a while.
Alistair MacLean has a number available, but not all of them (in the US). I maybe have to see about buying from the UK Kindle store next week when I am in London.
But this type of thing is why some revert to torrent sites. I admit I picked up a few Heinleni books elsewhere, but I buy them as they become available through other outlets.
There are a few other authors where this is also the case.
Hey, for someone in the UK are the 633 Squadron books available in ebooks form in the UK?