Conduct an online search for the fan club. There are so many fan clubs on the internet these days. Most of these are unofficial and are run purely by the fans who have nothing to do with the production studio or the production team of these TV shows. Look for the more followed fan clubs and if possible, find out the official fan club of X-Files.
Online discussion board can also be useful in this regard and someone can certainly point you in the right direction to find the official one out of the many unofficial ones.
Request to Join
Official fan clubs are often request only. So send in a request to join. They may require some basic information so be ready to fill it in. If there is an option available to send mail, let the admin of the club know that how appreciative you are of the program and how much you like it. In case the fan club is not online, you can mail the details that are required by them for scrutiny.
Wait for a Response
The request should by processed soon. The total time that is taken will depend on some factors such as the medium through which the request was sent. If it was sent through the mail, it will take longer to process.
Similarly, it is also an important factor as to how many requests are being received by the admin of the fan club at a given time. If they only have a handful, your request should be considered pretty quickly. On the other hand, if there is a back log or the club is getting many requests at the same time, it can take longer to be processed.