dotclue.org/t20 has a program to make the maps into PDF's, and a set of data to make maps from available. I strongly suspect that's just the assorted UWP's and sector, maybe subsector, names.
Domain of Gateway textual description is briefly covered in t20 Traveller's Handbook.
Alien Modules for CT often included a sector. Not all f them did, but ISTR Aslan, Vargr, K'Kree, and Hiver ones did.
Suplements 3 & 10 are sector books; the spinward marches and the Solomani Rim, respectively. (CT)
where: buy the supplements reprint.
Diaspora was released for MegaTraveller; is is a standalone folio product.
Where:
DTRPG as Secure PDF, IIRC.
The Regency Sourcebook has ALL the domain of deneb, both 1116 and 1200 stats. Some library data. TNE product.
DTRPG Again, DRM PDF
DGP's Traveller's Digest (OOP, Hard to get) has several sectors with writeups amongst its issues.
Challenge had an issue with a Hinterworlds sector booklet.
MegaTraveller Journal had the Domain of Deneb split between Map (issue 1) and data (issue 3).
In ALL the above, the vast majority is JUST URL's and a paragraph or so per subsector.
GT has "Behind the Claw", in gurps terms, some contradictions (mostly minor) with The Traveller Adventure (CT - Not in reprint yet), Beltstrike (CT - Not in Reprint yet), and several adventures (the adventures are in the CT reprints!). Niggling stuff, but be warned that there are some minor contradictions, AND IT IS ALL IN GURPS TERMS, and is usually a paragraph blurb per world.
Where: your FLGS or
SJ Games
CT, MT, and TNE sector products tended to NOT have large amounts of detail. A paragraph per subsector (if that much), 2-3 pages of library data, and loads of URL's.