This ruler has been one of my favorites for years; I'm sorry to hear how hard it is to find now. It does appear that it is no longer made.
Last year I asked That Patchwork Place to make a 12.5" one like their Bias Square 8 and they said they were considering it. Let's contact them with requests and encouragement!
http://www.shopmartingale.com/help.html Scroll down under "Martingale" for way to contact them.
Jan in VA