I am looking for posable "realistic" (i.e. not cartoonish) models of dragons. So far I am aware of, as available to the public:-

(1) Millennium Dragon. I already have this, but is it still available to be downloaded or bought?

(2) Daz Dragon. Where can I find this? Search on Daz's site leads to an endless list of stuff to have to wade through, mostly irrelevant, including a dragonfly, and costumes for humans, and something called a subdragon, and allsorts.

There are some dragons on Renderosity:

https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=87216&&

https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=65325&&

Thanks. What I got at those two web addresses was:-

https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=87216&&

This caused a fault remark "Your search - https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=87216&& - did not match any documents.".

https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=65325&&

This found a model called "Swidhelm's Skywyrm". It seems that setting its wing membranes needs the Cloth Room, which is something that I am not accustomed to. How could I set its wing membranes to fit at any random pose, not only the 6 poses that come with it?

The other https://www.renderosity.com/rr/mod/bcs/index.php?ViewProduct=87216&& is the Skywyrm Bull and they both require the cloth room for random poses.

There is a membrane tutorial included: Membrane Tutorial.pdf

Freebie dragons and a wyvern not cartoonish - from Dodger at sharecg

Dodger at sharecg

Here is a Freebie of a Dragon !

https://sharecg.com/v/94995/view/11/Poser/Summoners-Lucent-Drago

these are just a few of many that summoner made

All for Poser exclusive you might find something nice if you like Dragons

We're not supposed to link to competing sites, but DAZ has a bunch of dragons. The original Millennium Dragon is still for sale. There's also the Millennium Dragon 2. There's an LE version and a hatchling. The SubD dragon (with a LE version) could be used in Poser, but the appeal was the subdivision for DAZ Studio.

There's also the Eastern Dragon, which is a Chinese-style dragon. The Fork Horn Dragon, the Water Dragon, the Hammer Tail Dragon, the Long Tail Dragon.

These are all Poser figures, meant to be realistic. There's more that have a more toonish look, and a lot more that are DAZ Studio only. I believe the DAZ Dragon you mention is for DAZ Studio only.

Daz Dragon 3 is only usable in Poser with DSON ...

Free dragons are here:

https://poserdazfreebies.miraheze.org/wiki/Fantasy_Monsters

Have you looked at the Sixus 1 Dragonz? My personal favourite dragon, especially when you add the expansion set