Cocobolo would be a good choice, but I've also seen scales made from desert ironwood, pakkawood and others. For an idea of what can be used, check out the Dovo and Thiers-Issard razors
Classic Shaving.com - a great place for razors and shaving (and where I got my straight razor from, and the owner is a very helpful chap). The woods seem to be "moisture stabilised" - whatever that means.
The same website also sells pins and scales (if you didn't want to make your own) - go to the Maintenance and Restoration section.
I also used to frequent
www.straightrazorplace.com - a great place for all things shaving with sharp implements. I found a good article on there on how to replacing scales (go to the Help files -> Permanent Archive -> Great Straight Info -> Page 3 and download the handle making pdf).
Hope this helps, and good luck - it's a nice looking blade you have there!
Mark