I can answer for the more well known ones.
Schumacher still have early cars and prototypes at the office, some can be seen on Cecils interview on RCRacing
http://www.youtube.com/watch?v=FruLSZMQ_Kw
Gil Losi Sr. kept the prototypes, originals and trophies when he retired. Unfortunately they were destroyed in a lipo fire.
http://murrieta.patch.com/articles/f...arage-contents
Associateds prototypes and specials were kept by Gene Husting when he retired from Associated. He photographed some of the cars a couple of years ago and they can be downloaded from Associateds website
http://aedownloads.com/pdf/originalrc10.pdf
http://aedownloads.com/pdf/detroitrc10.pdf
http://aedownloads.com/pdf/australianrc10.pdf
http://www.rc10talk.com/viewtopic.php?f=35&t=16520
Gene Hustings display in his home, including the famous 'full size' RC10
http://www.rc10talk.com/viewtopic.php?f=77&t=17186
Finally, Genes son Curtis Husting with the original boxart RC10 at Team Associated.
