I actually had another member PM me not long after I posted that asking for them, and they are on their way to him now. I didn't realize there'd be such a market for them!
However, it looks like they are still available new, if you're willing to deal with Bill Evanoff's shenanigans. I gave up on buying anything else from him after I bought my headers in 2018, despite "not bad" experiences previously with other products of his...
Long version:
An "old time" member here who no longer posts (guitar maestro) was gearing up to produce a batch of MN12 specific long tube headers a number of years ago. After my headswap/build in 2013, I was holding out for him to make me a set instead of buying the Kooks, since I'd have to have my Trubendz exhaust kit modified upon installation either way (and I would rather only do it once). He sold off his set of MAC longtubes that he modified to use as a measuring template for building his headers, but they were sold to another member before I was able to save up the funds. As time went on he became more sparse on the forums with other life projects taking priority, and finally he told me it was not likely he'd ever get any longtubes built.
After that I happened upon SCP again and saw that Bill, who is the exclusive dealer for the MN12 4.6 Kooks, was not going to be ordering any new batches of them - supposedly due to dwindling demand. The price was steep but I needed headers for my combo, and with two sets left I bit the bullet and ordered one.
The first thing Bill did was tell me how much he charged to my card and that he wouldn't be shipping the headers for a week - which was a couple bucks shy of $900. I did the math and worked out that he charged nearly $50 for shipping and even added sales tax to the shipping costs, on top of the merchandise. Aside from the fact that he should have told me what the shipping charges were going to be ahead of just billing me for them, I decided that $50 for shipping them 200 miles was not worth it (I paid $45 this to ship these twice as far via the same carrier to the individual who just bought them from me, with full value insurance, and we all know rates always go up a few percent every year). Resultingly, I told him to NOT ship them, and that I'd make the 3 hour drive to pick them up. Then he sent me a several hundred word essay/sob-story telling me how adding sales tax to shipping was OK, that $50 in shipping charges was very reasonable, that he made a mistake in telling me they wouldn't go out for a week and that they did in fact get shipped that day, and that I needed to remember he had to pay to get them shipped from Kooks to him! At that point I decided I was done dealing with him since he was clearly not going to own up to or attempt to reconcile with me over the fact that he took more sales liberties than he should have - which caused me grief. In the end it wasn't as much about his making profit on the shipping costs as much as it was his rooted defense of his (IMHO flawed) position.
I checked the other day and sure enough, Bill changed his mind on "discontinuing" the headers, and has been ordering them in batches as demand dictates. Of course, with a nominal price increase.
Fast forward to this week, and the owner of the guitar maestro "beta" headers (still never installed or used), another former frequent poster here, PM'd me and asked if I would be interested in buying them from him. Sure enough I was! Once that deal was finalized, I was able to sell the 3/4 Kooks I had been holding onto with a bit of a sour taste in my mouth. That all happened in the last few days.
</rant>