Depends on the kind of main clan you want to join. Some of the older, more established clans have pretty rigorous application processes to weed out either leaks or people they don't deem to be high enough quality of a player for them (elitism etc).
However, there are also a lot more open/casual PK teams around that let anyone join. Groups like Divine Kings (very easy/simple app process), "Authority" (Lil Cards stream/open cc team), Skulled Revs cc, the 1500 total world team "Moi", etc. Some established clans (Violent Resolution, Vanguard, etc) also have a somewhat easy application process compared to some of the more serious clans like CT, Rev, DF, Rot, etc.
Those kind of clans may not be to your liking (low levels, low quality, etc), but they're a great way to get into main clanning if you don't know anyone in any of the established clans since people from said clans will hang around these teams and recruit off them.
Granted, it is still possible to get into the serious clans without knowing anyone, it just takes a lot of effort and dedication (constant activity around their forums, discord, speaking with ranks frequently, etc).
Good luck finding something.