The real 'speed nuts' are rubber encased steel. There are two sizes used on classic Porsche cars. Those OE look parts are readily available in the small size. The large size doesn't seem to be produced at the moment. But things seem to change weekly.
In the meantime, I found a rubber washer and a 'speed nut' and use the two parts together. It's not OE, but it's as close as I've been able to find for the time being and it's WORLDS better than this crappy stuff...
I can sell sets for the engine lid letters for $10. It takes 14pc, but I'll make the kit 16pc so there are a couple extra just in case...