I think that what you guys are calling "black" here is really green.

The standard Cameron tartan is red, with four green lines, and a single yellow stripe on the red feild. In a lot of photographic representations, the dark green comes out rather black looking. But trust me, it's really green.

But there is, in fact, a red and black Cameron tartan, and this is perhaps what Ron is referring to in his original post. It's recorded as tartan 1186, and is quite striking, in my opinion.

The House of Edgar offers this tartan in their "Old & Rare" range of medium weight cloth. They may be the only ones producing it right now.

Aye,
Matt