I think you can order a set of 4 new Square four con rods from Bennet Longman.
Mail to: bennet@ironhorsespares.co.uk
These are the same rods the club used to sell.
I don’t think you need to be a member to buy them.

Wanted: late 40's or early 50's rigid frame to fit 500 engine.
Who has such a frame laying around and is willing to let it go to help me complete a bike (re)build?