The Gecko Norns were created by Wafuru who converted the sprites from a Creatures Adventures breed and added a tail in order to make them look more lizard-like. They only come in one size.
The Gecko Norns occupy Norn slot G and can be downloaded at Adventures in Nornsitting!.
Have you been having trouble with Gecko Norn eggs being laid by the Grendel Mother? Don has made a patch to fix this - get it here, at WebPetz!