The list of "NLA's for airheads at authorised BMW dealerships has been growing for some time.
However, the availability of parts through independent suppliers tends to mitigate the situation, although some aftermarket parts suppliers are better than others just as some aftermarket parts are better than others.
Rob, you're fortunate to have Motorworks, Motobins and James Sherlock "on your doorstep" so to speak. I've dealt with Motobins for fifteen years from the other side of the planet, and still buy the bulk of my parts through them because I find them reasonable to deal with and their products generally are very good. On the few occasions there's been an issue, they have been quick to sort it out.
'76 R90S silver smoke
'75 R90/6 hybrid
'Skills are learned, talent is ornate.' Billie