i am trying to locate the original name plate for the above train , she was renamed THE ROYAL SCOT in 1933 , whilst the KDG name was transferred to THE ROYAL SCOT, the KDG was 3 years younger , and they needed a train of this class to take to canada/north america , , she was brought back for a total refit due to the inferior quality of the coal nearly was the death of her , i did find years ago that the kdg was preserved in 1962 and not scrapped

46152, as the loco became after Nationalisation in 1948 was withdrawn from service on 13th October 1962. What actually happened to the nameplates after that would actually be difficult to confirm.
Generally one of the two plates from a locomotive named after a particular Regiment/City or other body was presented to that organisation whilst the other would be sold off to interested parties eg railfans. Some of these plates are worth farily large amounts of money nowadays (the equivalent of $15,000+ in several cases), so some owners don't actually publicise the fact they have them. I know a couple of people locally who are in this category, one of them having some particularly valuable diesel and electric nameplates off locos built in the 1950's/early 1960's.

There are people, particularly the dealers/auction houses in the UK who have drawn up lists of known plates that still exist, though I'm not sure if they are available via the internet. Your best bet might be to contact one of the UK magazines like Steam Railway who might be able to feature your question to those who may be in a position to know.

EDIT - The Regimental museum is in Cardiff Castle, Wales - They might have a nameplate there http://www.qdg.org.uk/

As an aside, the original 6152, which swapped identies with 6100 "Royal Scot", actually made its return to the UK mainline last weekend for the first time since 1962......
https://www.youtube.com/watch?v=cdr2-tJr9ho

i served with the QDG and are museum does not have one of the name plates, she was not down as scrapped but preserved ,in 1962 ?? i have asked the question on their page why she was not replated and renamed to what she was first named , had no reply yet

During its recent restoration sufficient major parts were found to be stamped 6152 to finally dispel any remaining doubt that the loco known as 6100/46100 'Royal Scot' is really 6152 and the real 6100 (carrying 46152's identity) was scrapped in 1962. Quite simply the two identities were swapped for the N.American tour and never swapped back.
Ray.