As travelover said, unless you want to bust out some tile to change it, you're probably better off sticking with 8" centers.
There's another site that sells this type of fixtures:
Clawfoot Supply Co.
I am just about to place an order with them for a clawfoot tube shower enclosure. I don't know what your timing is, but once I get it, I'll let you know about the quality.
Here's an example of something similar to what you're looking for. The spread on the piping has a wide adjustable range (3-3/8" to 12-3/8")
They're a bit more expensive than what you'll find on fleabay, though.