The parts book for the Black Engine models is at the back of the Black Engine User Manual (PDF) 5MB.
Look through the sections below for Silver Engine parts, this is from a parts book actually for the Suzuki Exacta and some pages are not applicable to the Beamish - like frame and handlebars.
Open these files or download them as you wish. the first file is worth reading and it will show you in which of the other files you will find what you are looking for. The final file will give you a list of all part numbers for the RL250 and is a good source for reference