Try Volvo Genuine Classic Parts
https://www.gcp.se/en/
About 15 years ago they were the only ones who had the rebush kits for my B20E distributor. If you need parts for the advance mechanism I think you are definitely out of luck because even those were unavailable for the B18 / B20 15 years ago. You need to pony up the big bucks for a machinist to custom fabricate those parts if you absolutely need to stay original.
The default replacement part now seems to be the 123 distributor.