hi,here's one on ebay 231074491229 but you will have to enter your own data.
The plate usually contains the army registration number,the overhaul date and a
workshop ref number where the work was carried out and the date.This info may
be in the key cards,you will have to ask nicely.Also your frame number will be helpful
cheers Rick
email (option): richardholt@rocketmail.com
Those plates on ebay are the large post war plates. Sometimes found on or in motorcycle tool boxes with the corners cut off. Here is the type used during the war (at least late war) I don't know when the started using them and this one is just post war. Ron
email (option): ronpier@talk21.com
Hello Brian,
Your (post war) army registration number is 15YE69. This number "replaced" the war time census number that was painted on the petrol tank. I guess you know that this data plate is a post war thing... It was usually rivetted to the toolbox lid.
The repair plate in Ron's post was only used at the end of the war, and shortly after the war. I don't think that repros of this one are available.
The plate that can be found on the rear mudguard is the contract plate. The numbers on the contract plate are the contract number under which your bike was made and the spare parts catalogue reference number for this contract (respectively S/2603 and 35 for your frame number, but I'm not quite sure about your engine number's origin... 
). S contracts had a steel contract plate, here's another thread about these plates.
Jan
email (option): wd.register@gmail.com