I have a defunct Becentre 2000 in the loft.
There are some fundamental issues with it that make it one of the least popular B&O systems.
Firstly it was made in Japan, apart from the turnable components, so many B&O enthusiasts don't see it as a real B&O system. This also applies to the 2002 and 2200.
There are better B&O systems from that era that can be had for not much more money.
It isn't nearly as well laid out internally as many B&O systems and is a bit of a pig to work on.
There is an outside chance that Martin (Dillen) will have some belts but they won;t be easy to fit. You could get B&O dealer to do it for you but it may cost more than your system is worth.
I would advise doing one of 2 things.
The Beocentre 2000 is not a great B&O system but is better than many competing systems from the time. Simply use it and enjoy it without the cassette deck.
Alternatively if the cartridge on the turntable section is working well, remove it from the system and sell it on Ebay. Dispose of the remainder of the system. If the cartridge is in good condtion it could fetch anything from £25-£50. Then put the money towards something like a Beocentre 5000 or a Beocentre 7000/7002/7007 or a vintage B&O seperates system.
Simon