The Leman Russ model was rogue trader-era and terribly bad. He looks like he is doing the hokey pokey and faintly marine-like. That is because he was created as Sergeant Russ, a basic character. As the fluff compendium were released and the game progressed, he grew into the primarch of the SW. He then became this super-human myth after he was just supposed to be the progenitor leader.
So, the model is terrible and looks like a very very shitty Ragnar Blackmane. It was never meant to be the russ we know and love.
There HAD to be some type of rules for him, but nothing like what you'd want or think.
NOTE: You might be able to Google him or see him in bits order catalogues or GWs archaic model online store section.