You cannot get a new B&O stylus so you have two choices:
1. Risk buying on on eBay - these will all be 20 years old + and are possibly no better than the one you are replacing.
2. Get a Soundsmith one - the cheapest one is the SMMC20E which would be a definite upgrade to the MMC20S. It is however - are you sitting down - $230.
I would recommend the latter but it will depend on how much you play your records!!