Mark,
I can't help to answer your first question, but am looking forward to seeing the answer as well. The ones I have been able to buy in the past have not been as big as the original flyer ones I was looking to replace.
But on your second question: I usually cut the old brad with wire cutters to remove it. The harder part us crimping the new brad, because the ones I have been able to find are much harder than the originals.
Aflyer