There are hundreds if not thousands of pronounceable 5 to 8L .com domains currently available. 5-10% of them have been registered for 8-10 years before being dropped. Most of them could be called 'brandable', but very few of them are really 'desirable'.
There are ~50k words in english, so there are some 2.5 billions two words combinations and I don't have statistics. Most are not worth. Most 'related keywords pairs' are simply called 'keyword domains' and when available they are sold through auctions.
I encounter very few expiring domains composed of 2 english words, and usually they are unrelated words. Some could be turned into brandable with a lot of efforts. Imagine bluestair, starelephant or something like that.