Is it difficult to replace a broken extractor?  Are there instructions anywhere?  Can you buy replacements through Del-Ton?  Thanks.

Provided you can seperate it from the Bolt Assembly, it is no big deal.  You should be able to get a replacement from a number of various sellers.  

As you asked about Del-Ton here you go:

http://www.del-ton.com/nw_bolts.aspx

CSP

At the top of the Maintenance and Cleaning Forum there is a link to a page with directions.

rj

Disassembly

1. Remove the firing pin retaining pin from the bolt carrier.

2. Remove the firing pin from the rear of the bolt carrier.

3. Push the bolt back into its locked position.

4. Turn the cam pin 90 degrees and remove it from the carrier.

5. Remove the bolt from the carrier by pulling forward with a twisting motion.

6. Remove the extractor from the bolt by pushing its retaining pin out and lifting off the extractor.

Reassembly

1. Install extractor with spring and pin into place.

2. Replace bolt into bolt carrier with a twisting motion. Align the cam pin hole in the bolt with the hole in the bolt carrier.

3. Install the cam pin and rotate it 90 degrees.

4. Pull the bolt forward to its unlocked position.

5. Install the firing pin and firing pin retaining pin.

The directions posted are fine.
I only do it every now and then,but you should know how to tear down the bolt this far for a complete cleaning.
Sounds like a bunch of steps but once you do it with the list of directions on the workbench you will see how everything fits together and from there on in you just do it from memory .

what the others have said works, really basic