Have you checked with miles over at trade winds in gulf breeze that dude is the man for having older stuff like that laying around. Him or Numrich are my goto places for older gun parts
I just had this problem with a 686 I got in a trade. I had to take accurate measurements of the total length, blade to screw hole, and screw hole to end of leaf. I finally found one on e-Bay of all places. I had contacted Brownells, Numrich, and Smith with no luck. I thought I had found one at MidwayUSA but it was for a newer model so I hit up e-Bay and Gunbroker. e-Bay came through for me. Here's a link to a listing from the guy I bought from:http://www.ebay.com/itm/191005869160?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 His prices very quite a bit and I didn't pay anywhere near what he has on this one. Good luck!