Not
quite true
I know of various dealers other than Mclaren who have sold F1's [notably Taylor & Crawley, Tom Hartley, ELMS Collection etc] -it won't be illegal to sell one outside of Mclaren otherwise all these need to be doing some time inside.
If you can find an F1 for as cheap as £3.5m I'll be first in line please
I'll let others chirp in to correct some more....