The Lurent are a relatively recent addition to the Traveller Universe. I, for one, had never even heard of them until today, and I've been Travelling since 1978. In fact, when I first read your post, I assumed you were mistakenly referring to the Luriani.
That said, the Lurent appear to be a creation of Mongoose's Deneb Sector supplement (2012). The vast bulk of material written about the Spinward Marches predates that, and so nothing would appear in there about them.
There is a new Mongoose supplement, Behind the Claw (2019), which details both Deneb and Spinward Marches sectors. I don't have it, but I would bet dollars to donuts that the Lurent have been retconned into a few Marches worlds in that.
Of course, this should not be confused with the earlier GURPS Behind the Claw supplement, which is about a decade and a half older than the Mongoose version, and as such does not have anything at all on the Lurent in it (which I can guarantee to be so, because I have it).
If I read the Traveller Wiki correctly, longtime COTI member robject had a role in creating the Lurent; if he sees this post, he might jump in with further insight on how far they range outside of Deneb.