Hi Alan,
The Beogram 1000 was the first turntable to carry the "Beogram" tag. It is a "old" model- manufactured between 1965 and 1973,so I think it's going to be hard to find a cartridge at all ,let alone what it might cost.
Just to clarify, you say that you need a replacement stylus- does that mean you have the cartridge?
The cartridge you're looking for is a SP6/7.
An American company called Soundsmith have their own equilavents of B&O cartridges ,but don't manufacture a SP6/7 . They can however re-build your own cartridge (if you've got it that is) and put in a new stylus.This would cost $150US or $250US or $350US depending on what specifications you go for .
The only other thing I could suggest ,would be to advertise in "Beoworld Private Wanted".
Hope this helps
Regards
Noel.