No Trig System entry Filaments for sale

As the subject says the filaments that are required to enter / exit Trig system space are not for sale on market and there is nothing in contracts, how do you get them

From trig space, and there are filaments for sale for leaving trig space, i got like 20 of them myself nice and cheap, most people are buying them with plans to go yeet in to t-space only they haven’t realised there really isn’t anything of value here