I have gotten my stuff from these guys.. They also do class panels.. I have never had a magnet fly off before. The stuff they use......I don't know if it is higher quality or not....but it sticks on the car very well, and doesn't come off until you pull it off.
You just need to take care of them and store them flat.
I think my problem may be that the pre-'99 body has more contours on the side. The one at VIR was the second magnet number panel I've lost. But I was there with 2 guys who had the magnetic panels from soloperformance on '03's, and they stayed on.
It's just the price I have to pay for those sexy body lines.