My understanding on the large cores anyway, is they are only produced from one plant in Canada. It was supposed to go down for an overhaul sometime either late last year or early this year, can't remember exactly.
Either way once they shut down there would be no new cores available until they came back up IF they come back up. If memory serves the factory was pretty darned old, so who knows.
I know I am sure working hard to recover and reuse what I have. Come to think of it I have tired to do that with most of my other lead as well. Could it be I just like pouring them up more than I like shooting them? Naaa, I just haven't been finding the hogs lately like I used to, that's all.