Have you googled it? Also, I'd try a bath specialty store.

I have had little to no success. What would you google?

Try this link.
http://www.historichouseparts.com/pdshop/shop/item.aspx?itemid=11141

Is this an old Crane unit?

Can I ask why you are replacing the valve? Is the chrome failing? Dripping? Or just tired of the look? Often these unit are proprietary and some real engineering/fabrication will be involved to put something altogether different in its place. Out here in Berkeley, we have a wonderful resource in The Sink Factory - (sinkfactory.com). Super knowledgable in the old stuff.