Hi jd
The best method for securing spare parts usually involves cannibalising a second unit which you will first have to find. Fortunately BM3000s are reasonably common and easy to get hold of but you might end up getting one that is better than the one you have.
In your case, I have two comments:
The volume control slider is normally repairable unless it has been very badly mangled. What is wrong with the one that you have. They can usually be split in half, cleaned and repaired without too much difficulty.
The pre-tuner is probably going to be very difficult to find. Have a look at the recent thread which shows how to make one yourself. That is a very satisfying project for something that has no impact on the audio quality of the unit.
Hope that helps
Regards
Geoff