Here are the dimensions of the pickguard used on the Yamaha SA-20, SA-30 and the SA-50. All other models have a different pickguard. Download the PDF file, print it such that the measurements shown below match the measurements on the printed copy. Ideally you obtain the correct 5 ply pickguard material.
Download this PDF file:
Below a few photos showing the pickguard from different angles;
Good luck.