Who says so? I got a spare belt within three days of ordering it from Fox's in Ipswich last year. Much cheaper in fact than trying to source one from elsewhere as they are much longer than 'off the shelf belts'.
I beg forgiveness. I had read elsewhere in another thread that Raymarine did not sell them anymore and assumed it to be true.
But having called Raymarine they are eager to sell me one and I hope it will arrive tomorrow - or at least in time for the weekend.