I really think you've got this confused
The Nokia UK website directly links to Amazon, clearly indicating that Amazon are selling these legitimately, not as "grey imports". There are any number of other retailers also offering these online, many through Ebay, some direct.
I think you'll find the reason why few other large outlets have them available is two -fold
First the operating system. Symbian is dying, and the mobile phone network companies know it. They are not going to provide tech support training for a dying OS. They will not bundle any phones with their services which require specialist training for a dying operating system for just one model of phone. They have enough to worrry about with iOS, Android, Microsoft operating systems which all have a future
Second, Nokia is on its last legs and the network companies know it. They're not going to commit themselves to reselling product from a company that could go smash.
All Nokia have as an option is to try and sell these as SIM-free models on the open market. But few people can afford to purchase full price SIM-free phones, so sales volumes are going to be low, especially as its an unpopular OS anyway.
So overall? Its a dead end design using a dying operating system that few people want. That means minimal sales