I found a few pictures of a 54mm Necron, but wasn't sure if this was a GW figure or a combination of figures. It looks legit, but the description says it was based on a conversion of at least 2 models.
(http://thumbs.worthpoint.com/zoom/images1/1/1015/04/inquisitor-54mm-collection_1_b7c24af7a6d0f6b9fcd20e283c5d7a86.jpg)
I have got one of these, bought from Ebay, where they seem to crop up fairly regularly. They seem to be a fan-produced figure. Certainly not GW and they do not appear to me to be based on any GW figure or a combination of figures. I would love to know who designed/produced them if anyone knows more.
It is a decent sculpt and has been well moulded.
D