It rather depends on what is left of your MMC20S. Axel can repair these and put a new cantilever and stylus on for about €80. The alternative is a new Soundsmith one which will be twice that. The MMC10E will fit though this is a US model not seen much in the UK. The following will also fit:
MMC3000, 4000, 5000, 6000
SP15
MMC20S, 20E, 20EN, 20CL.
Do bear in mind that in the case of the BC2000, the cartridge is the most valuable part. It is definitely looking at car boot sales as old B&O does come up and a BC2000 with cartridge may well be considerably cheaper than a cartridge alone.