I was perusing the Solegends website and I came across this gem:
http://www.solegends.com/citcat89autumn/c89aut-072117-3-02.htm
Apparently games workshop in their distant past DID make a specific minature for a rogue trader. He has a powersword and a bolt pistol, and what appears to be a long coat, cargo pants and a 2000 AD style Shoulder pauldron.
Back in the day eh...The best I could think for a Rogue Trader-ish minature from the GW range is the one for Karl Jerico. I seem to remember the classic combi weapon assassin on the page but I never seem to remember the rogue trader being about, and yet there muts have been as many about because they were sold in the same blister pack. Unless of course as is the way of GW it was renamed Imperial guard captain or something.
Any of the older afficianados possess this minature. I doubt its going to turn up on e-bay...