However, since they went so far out of their way to point out that their people are not the Dalish... the next logical question is: Where are they?
We already know who they are talking about - ancient elves, but not where they are. If all of his ancient peers were sealed away, unreachable, why would he tell Abelas that they can be found? And if not all of them were sealed, who remains free? It's possible Solas was referring to more Sentinel-like ancient elves, tucked away in a temple someplace. However, Abelas did specifically ask, "Elvhen such as you?"
There might be other temples out there; I can't imagine Mythal is unique in her use of immortal sentinels to guard her temple. The places where the elves slept within the eluvian network were in bad shape in Masked Empire, but there might be more of them as well.
Felassan is also clearly an ancient elf, and he's definitely not holed up in uthenera. His dialogue implies that there are more out there like him (not necessarily bound sentinels like Abelas), and they're dangerous. That's...about it.
My personal headcanon is that the "elvhen such as you" line is where Abelas recognizes Solas as not only a fellow ancient elf, but as the Dread Wolf. He just doesn't say anything because he doesn't feel like it's his place to say anything, or he assumes Lavellan already knew. But that's just headcanon 