Would have been useful to state that as explicitly as you have just done but in your opening post.
The last TVs I sold with speaker terminals were Pioneer and Loewe plasma sets from 2005~2008. Can't recall ever seeing speaker out on LCD/LED sets, and nor on OLED either.
Second-hand, off the top of my head:
Monitor Audio BX2 or Bronze 2
KEF Q- or IQ- series
Wharfedale Diamond 9.1
Dali Spektor 2
Tannoy Mercury-series
Mission LX-series
The list isn't exhaustive. There are plenty of reviews online for used speakers. Treat the reviews with a pinch of salt though. End-user reviews can be less than objective and professional reviews can be overly-nitpicky. You're really just trying to sort the wheat from the chaff and eliminate any speakers with character flaws or reliability issues.
New
Wharfedale Diamond 220 (£99/pr)
Q Acoustics 3020 (c. £100/pr)
Fine F300 (£159/pr)
With either new or used I would suggest keeping an eye on the sensitivity figures. Small bookshelf speakers tend to be low (82-84dB not uncommon), where as better speakers might deliver 87-89dB. That might not make much sense until you realise it could be the difference between the amp working twice as hard for the same volume level on the lower-sensitivity speakers. The amp.inside the TV won't deliver oodles of power, so it makes sense to use it wisely.
Sensitivity tells you nothing else about the performance of a speaker though. It's a bit like the mpg of a car. You know how far it will go but nothing about what it's like to drive it.
