After months of trying to find a reliable manufacturer who would even come close to my insane price requirements, I'm pleased (and relieved) to announce that the Series 1500 and Series 1000 black Delrin rail buttons are back in stock.
For those that don't fly stuff large enough to require the Series 1500 buttons, consider this... a Series 1500 button and a T-nut make a perfect (and inexpensive) standoff for the Series 1000 compatible rails. :)
Matt Stum NAR#73280 L2 railbuttons.com