I'm glad you liked the idea.
I didn't quite understand: do you not know how to extract rider models from mods, or do you not know how to create a different dragon for the rider?
Regarding changing the dragon, I completely agree. Although changes can be achieved by playing with colors, for example, adding green elements instead of yellow ones, and making the dragon itself darker…
I am currently browsing all forums trying to find a modder who could bring this to life. It would be good to find someone experienced for whom this wouldn’t be difficult and who knows how to do it quickly and easily.
If you know anyone on this site, maybe you should suggest this idea to them. However, even if a modder is found, there is no guarantee that they will be interested in it.
I have already posted an announcement somewhere; let's see if anyone responds.

Yes, and regarding mods:

Here I saw a rider on a horse /topic/at/197835/

I found a rider on a dragon in this mod - http://rutracker.org/forum//topic/2629561/

The mod itself is a very high-quality collection with a huge number of new and interesting units. In addition, the mod has many other changes. Highly recommended.
I am now trying to contact the person who uploaded it because he wrote that he knows people from the Russian community who are directly involved in creating models.
Let’s see…

PS Well, and if you manage to achieve something, that would also be great.

PPS During my search, I came across the website of the team that developed the units, but as it turned out, this is not a Russian community at all.
http://heroescommunity.com/viewthread.php3?TID=27275
There is a list of creatures at the link. Number 284 is the rider on a dragon.