Bell Metric
Car Snob,
With a name like that it is a little hard to give out info but I am feeling generous tonight. I am surprised no one has told you about Bell Metric as in bellmetric.com. They have it all for fasteners, provide good service and are very responsive to any questions. Another good source is Walloth & Nesth in Germany. W&N has complete fastener kits for CSs although I don't know if they cover the 2000 CS.
The second part of your question and perhaps the hardest is identifying the fasteners you need. I would recommend a BMW white parts catalog (2 volumes) ideally for a 2000 CS but because a number of body parts are the same as the 3.0 CS, possibly, a 2800 or 3.0 CS parts catalog will help you solve some of the questions. There are ones in print and you may get them on CD also. I think they have more detail than Real OEM and Penske and have the unique feature of being able to cut and paste (literally). I have used the parts catalog extensively for my build and the detail, down to nut, bolts and misc, is incredible.
I hope this helps.
Regards, Jon