most if not all of the parts are still available from
www.dewaltservicenet.com additional options are to see what parts exist at your local service center. You can also go the other route and buy drills, there are places online that you can buy complete refurbished drills.
http://www.toolking.com/dewalt-dc930...tool-with-case
The xrp line that the NBD was based on was discontinued a year ago the new drills can be modified in a similar manner with some experimentation.
If you do plan to go the route where you take drills apart, be aware that you actually need more parts than 1 drill can provide. Additionally if you are going to do a machining setup to bore the sun gears for pressing on CIM motors I recommend making as many as you can all at once. Trying to find a WIRE EDM will be very helpful as powdered metal does not machine well.