Hard to come by, Tom. So many were replaced by the better shocks that came out in 1931. In some cases, they were even replaced with tube shocks, like on my dad's boattail (I just bought a pair from a 726 parts car and sent them to San Diego to get rebuilt).
However, I just saw a pair sell on eBay for about $115. I'm sure they would have needed to be rebuilt. They pop up once in a while. I've seen two sets within the last six months on eBay.
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MT2MB