If you subscribe to his online newsletter the "Kirban Inner Circle" you'd know that all those discontinued items are no longer available simply because the manufacturers (GM or otherwise) have stopped making them. He's always on the hunt for new sources for OEM type replacement parts. In fact, he's put a few things back on the market and it sounds like he has more in the works.
but that "capped crap" was what the GN's (and all GM vehicles) came with back in the day. without them, you'll miss out on the fun of having those little caps slide off and jam in your lugnut socket!
I worked for Discount Tire back in the early 90's and trust me, those GM capped lugnuts were inspiration for much profanity out in the bays!