More seasoned veterans please correct me on the process, but I believe a new CRL is driven by somebody, or a team of somebodies, researching the details and making a costume which is then used as the CRL model, working with the Legion membership officer. I'm guessing the Pretorian Guard costume would be in the Sovereign Protectors detachment same as the Royal Guards, so there might be some WIP / CRL development posted in those forums.