I like the idea of using riders from the terradon kit, but unless you resin-cast a bunch of extras that would be a lot of kits to buy. But you can always try bitz websites.
Only good example I found was the traditional Tichi Huichi's raiders, and you would have to get those on ebay at this point. Plus the models are a tad dated, but can still look awesome when painted well.
View attachment 27182
Also found this gem; his horns look like something out of the beastmen gors kit. Could be simulated using some extra green stuff to make your cold-ones more... spiked. (
link- Inxi-Huinzi)
View attachment 27178
The only other conversion I found was from
dakka dakka, and it was only of a single skink on the older metal versions of the cold ones:
View attachment 27179
It looks like the artist just made a "saddle" for the skink on top of the cold one's back with some clay/green stuff for the skink skirmisher to sit on. Pretty easy conversion to make; with this method all you would need would be some skink skirmishers and some leftover cold one bodies (which would be slightly easier to find on bitz websites than terradon rider skinks I think).
Good luck if you decide to attempt this project, I would love to see more examples of skink cavalry.