I have one original blue plate registered with my 71 240z, how can I get another exactly the same one for the front? I checked some licence plate maker, and they all say it is not legal to use it as a real licence plate, any idea?

I would think that if you had one made and it looked close enough to the original, no one would even notice. Especially if your car is already registered with that plate number.

But who make one that is close enough to look "real"? does anyone know?

Well there's this place but the problem is that for some reason, probably legality, the won't ship into California. And, at $75, they are a little pricey for my tastes. My nephew has a 69 Chevelle and basically had the same situation you're describing. He had it shipped to our cousin in Arizona who in turn mailed it to him. He's had that plate on the front of his car for a couple of years now with no problems. Here's the link: http://www.licenseplates.tv/prod/1969_california_stat_1569.html

was the qulity same as or close to the one from DMV?

From what I can tell it is. He mentioned something about the font being slightly different but I couldn't tell unless they were side by side except the replica looks newer than the original one.

www.darrylsplates.com

I've used them for restoration before, and they can make "original" plates.