The obvious answer is SK Grimes. If your short on cash you can try to make one yourself. Focus on a gray card and meter it through your ground glass as you close down the aperture. Mark each whole stop on a piece of paper you afix to the aperture area. Take this piece of paper and scan it, then open it in a digital editing program and then put the actual aperture numbers in digitally where you marked it on the paper. Print it out and your good to go.
I copied a scale, re-drew it more clearly and sent to a fellow APUG member last year, evidently it worked perfectly. (I think it was via another Forum though). I'm fairly sure it was the Symmar 210 scale, I'll look but give me time as I'm in transit for the next couple of days.
My thought was for an anodized aluminum plate stuck on with double sided tape and marked with calibrations using a scriber after measuring (as has been described above) was done.
I thought I saw aperture scales offered by B&H at one time. maybe I'm wrong but it mgiht be good for you to check.
Also, what about asking Bob Soloman? His company sells them, I think.
Other option might be the Schneider repair place in CA or NY? I think it's called 'Century' at this time. Find them under 'repair' or 'service' at the Schneider web site. My experience with them is that a phone call to supplement a email is best method to get their attention.