So Rim Jang Kwon was a requirement for Chil Dan in the World Tang Soo Do Association. My black belt manual, which I received in 1995, lists this form. A new and updated manual does not list this form any longer, but it has been replaced by Sae Jang Kwon.
The word directly from the senior masters is that Jae Chul Shin is completing a 6th and final book which is to detail the upper level forms. His 4th Book detailed the forms needed for Sa Dan, so this new book may detail Sae Jang Kwon. I've never seen it, but I am curious as to whether So Rim Jang Kwon influenced Sae Jang Kwon. I'd like to ask the senior masters about So Rim to see if any still do it.