i am looking looking for a used mag and to get one repaired i have a fairbankes morse on a general gg it is just spaining and not fireing i never have worked on one of this befor it is a fairbanks morse type j mag
if you have the right mag you would be better off repairing it than getting another one .replace the coil,points ,and condensor.that will usually fix them. you can clamp it in a vise and spin by hand to check. also the points on a mag must be perfectly clean to get a good spark.
good luck
walter