L.A.B. said:
If original, they will be an asbestos compound so probably haven't been manufactured for several years.
Unless you are determined to replace with NOS original, then perhaps consider the "High Friction" RGM MZ Gold shoes instead?
http://www.rgmnorton.co.uk/buy/rgm-rear ... d_2471.htm
These shoes are awesome. My only issue with them is to clean them with brake cleaner every spring and wire wheel the drum for a summer of the best rear braking for stock brakes available.
These shoe, if kept clean, really make stock rear brakes acceptable.