The Nintendo Switch Online + Expansion Pack has been met with all kinds of criticism since its release, with people describing it as laggy and challenging to play N64 games on a Switch controller. This has led the trailer for the pack to now be Nintendo's most disliked trailer of all-time, but despite this response, the N64 Switch controller that was released alongside the pack has been flying off shelves.
In both the UK and the US, the controllers are already entirely out of stock, and while the UK product listing for the device doesn't mention anything in particular on this matter, the US listing reveals that there will be no more stock for the controller until 2022.
On both the UK and US page, the controller was limited to four units per customer, and only released on October 26. Considering the US will not be getting any further stock, it does seem unlikely that the UK will be getting any further stock as well ahead of 2022, meaning if you were looking to nab one of these controllers for Xmas, it's probably a good idea to start searching for something else.