Originally Posted by _cy_
not cheap is an understatement on top of extremely hard to find!
it's worth noting that original BMW brake shoe material can get extremely hard. either from age and/or very hard to begin with. while it's normal for brake drums to wear a little. most of the wear needs to come from brake shoe materials.
assuming your drum is still within tolerances... to save what left of your G/S drum. take your drum and old shoes to a local brake/clutch repair shop. find one that will custom fit shoe to drum. if there's wear on drum, thickness for shoes needs to be slightly thicker. reason is max braking occurs at beginning of brake rod travel. when brake cam is in optimal position.
new shoe material will be much softer than OEM. much rather brake shoe wear vs drum. had no clue just how hard shoe material had become. until I tore into my G/S drum to track down why my rear brakes were so underpowered. getting brake shoes relined with slightly thicker/softer brake shoe lining fixed problems of excessive drum wear and lack of braking power.
That is a very good suggestion - I'll be following that route when the time comes for my rear wheel to be dealt with.