Well the black stuff you are referring to, I think can only be had online. And even then I would not know where to look for that. You might have to goto 3M's website and inquire on where you would want that.
My car is that dark metallic blue and it really doesnt show up unless you are looking for it. And like Toasty said, I simply got two types of the tape, one that is about an 1" in width and the other was like 1/2" in width. I used different types for different applications obviously.
The picture below is one of the badges I had to resticker after removing the black paint from the background. It took some time to cut around the GTX but it came out pretty good. Even at a side angle you really cant see the tape in the 2nd picture.
PLUS you can always use a black Sharpie to cover over the grey edges of the tape. Granted I have not tried that, but I am not nearly as pickie as you my friend
That looks good even too me. I'm not picky, I just expect nothing less than perfection. Which is why I probably shouldn't attempt this. I hate to be mad at myself.